Now here is my response to her:
How many witnesses with what sort of evidence would it take to be convinced that there is a God? Myself and 10 other people, all of different faiths, each missing a limb, and one of them Christian. Each of those 10 people will, in their turn, pray to their respective deity that their missing limb be spontaneously regenerated instantly. When the Christian's turn came, if this did indeed happen, without any other possible explanation, then I would believe in God.
As much as people like to point to the power of prayer and all of the people who have witnessed that power, they are deluded by the power of coincidence. Not prayer, coincidence. A church group prays for a member of their congregation who has cancer, and has been undergoing chemotherapy and surgery, and the cancer goes into remission. Did God answer their prayer? No. Prayer is not a vital element in the treatment of cancer, however chemo and surgery are. It really shouldn't be a surprise that the person recovered, since reality based steps to stop the cancer were being used.
However, if an amputee were to spontaneously regenerate a limb, there could be no other possible explanation than the existence of a God who answered that prayer. However, this has never once happened. No one, ever, has spontaneously regenerated a limb. When you take away any ambiguity as to whether or not prayer was the cause of X happening, you will find that prayer never influences X in unambiguous situations.
Only things that would have been possible in the natural course of events (even if not very probable), are ever answered by prayer. But if we know such things CAN occur naturally, there is no reason to get excited when that natural occurrence merely coincides with a prayer. God never does anything that only a god could do.
Even in the case of something happening that seems to defy all realms of possibility, we should remember that we just because we don't know what caused X, doesn't mean X was caused by divine intervention. It just means that we do not (yet) know what caused X. People have believed throughout the years that various natural phenomena, i.e earthquakes, eclipses, comets, floods, tsunamis, wildfires, etc were caused by gods or by God, yet we now know all of this to be false. If we assign God as the cause of the unknown, then when the unknown becomes known, we really just look foolish.
Going back to prayer, it is also crucial to point out that every time a prayer is not answered, Jesus has broken his word.
If you believe, you will receive whatever you ask for in prayer. [Matthew 21:21]
If you ask anything in my name, I will do it. [John 14:14]
Ask, and it will be given you. [Matthew 7:7]
Nothing will be impossible to you. [Matthew 17:20]
Believe that you have received it, and it will be yours. [Mark 11:24]
For truly, I say to you, if you have faith as a grain of mustard seed, you will say to this mountain, 'Move from here to there,' and it will move; and nothing will be impossible to you. [Matthew 17:20]
There can be no ambiguity as to what is meant by these passages. Jesus says you will get what you pray for. There's no fine print. And this coming from three of his Apostles, so it's not like they didn't know the guy. Plus, there is no evidence that any mountain has ever been moved by prayer, whether by believers or Jesus himself. What explanation is there for unanswered prayers then? Here's two possible explanations:
God exists, and God answers prayers, but for some reason God chooses to ignore the prayers of amputees (or prayers to move mountains, restore brain tissue). We don't have a good explanation for why God acts this way, and it does seem to contradict what Jesus teaches about prayer in the Bible, but clearly God has his divine reasons.
God is imaginary. If God is imaginary, then he does not answer any prayers. Therefore, the prayers of amputees would go unanswered too. The explanation entirely fits the problem, no ambiguity, no paradox, no contradiction. It also explains why other prayers for medical miracles don't come true (people born with Down Syndrome will not change because of prayer, people who suffer significant medically incurable brain injuries do not see their grey matter suddenly replenish itself whole and functional at the request of believers, etc). These are all things that could only be accomplished by God, yet they do not happen, ever.
Similarly, other non medically related events that could only be produced by God do not happen either. If a church prayed that the Titanic would be suddenly raised from the ocean floor and moved to the top of Mt Rushmore, it would not happen. Again this is something that could only be done by God, and yet no matter how many people or who they were, it would never happen. This is in direct violation of what Jesus explicitly promised in the six passages above, as presented by those personally selected by Jesus himself to spread his message. How could Jesus then be wrong?
If your response to this is that we are not supposed to test God, then don't believers violate this every single time they pray? If some prayers are "testing God", then all are, as they all ask for God to do something for the person(s) praying, and God either does or does not do it.
Here's another problem I have: why/how can an all knowing and all powerful God as presented in the Bible be limited to the knowledge of the primitive people in the story? Instead of explaining all kinds of purification rites for illness, discharge, infection, and menstruation does God not explain them in a way that is helpful? Why didn't God teach them about microbes, sanitation, sterile dressings, antibiotics, and the female reproductive cycle? Why does God view women with the same misogynistic contempt that the primitive men in the Bible do?
Why does God's worldview always coincide with that of the believer, no matter who they are or what they believe or what period of time they are from? And why has believers' perception changed, so that they can attempt to explain away explicit passages, in both the old and new testament, that say that women are subordinate to men, and are to be quiet, and not have authority. Why does God all of a sudden understand what is actually the right thing to do? Is he no more intelligent or morally grounded than humans? If so, I would argue that such a being is not, in fact, God.
The Old and New Testament also point to the fact that God, and his son Jesus are ok with slavery, yet this also only reflects the opinions of the people in the Bible. Now that WE believe slavery to be wrong, believers also think God must too. Don't you see what is happening here? It is sometimes known as SPAG, Self Projection as God. This is why no two believers will say the same thing when asked what faith and God mean to them. It means whatever we want it to believe, because we are creating an all powerful deity in our minds who is cool with whatever we are cool with, whether it be peace and brotherhood, or murder and rape, the Bible can be shown to support them all, thus providing a false validation of the person's SPAG.
SPAG also happens at a more general, public level. Even if believers would not give the same definition of God as the next person, they would probably include words such as "loving", "all-powerful", "all knowing", "savior". This is because believers in general want to believe that some cosmic superhero is right there for them, whenever they need them, who thinks like they do, who likes (and ignores) the same Bible passages, hates (or sometimes loves) the same types of people, and if we worship this cosmic superhero, he will share his powers with us by granting us eternal bliss (whatever the believers definition of this may be).
This is also used as the Christian means of Morality. Because of Original Sin, Jesus had to die and be resurrected, and we have to work to follow his laws, and confess our sins and faith in the Savior, and if we do, we get eternal bliss, if not, eternal punishment (note:eternal punishment for finite sin is a little harsh for a benevolent being who loves all of his creations).
Believers have to do good things in order to avoid eternal punishment and gain for themselves eternal bliss. This makes the motive for doing good things selfishness, as it is done to save the believer more than the person for whom good is being done. If you help a disabled veteran in a wheel chair, who wheel has become stuck in a street drain, and who is unable to dislodge it, the veteran is able to go on his way for the time being. You however are getting points towards eternal reward, which is infinitely more good for you than your help was for the veteran.
Yet, those who do not believe, such as myself, are not causing violence in the Mid-East (that has been going on for essentially millennia), are not running rampant raping, stealing, and killing anything in sight, crashing planes into buildings, launching "Crusades". Atheists are capable of being good people without threat of punishment or promise of reward. They do good, because it is the right thing to do, not because it will benefit them for eternity. If it is possible for people to be moral and do good things without faith in God, then Occam's Razor suggests that we remove that which is not necessary. That which is not necessary is, in the case of morality, God.
The Atheist would assist the disabled veteran, not out of fear of punishment or hope of reward, but because he wishes to show another human being consideration. Perhaps he even feels admiration for the disabled veteran who risked life and limb, and wants to show appreciation for that sacrifice. It is entirely selfless. "Do unto others as you would have them do unto you" isn't a Divine Proclamation, it's just common sense.
There is only one possible explanation for what I present here that does not contain contradictions or inconsistencies, create a paradox, explain away, rationalize, ignore, or alter evidence, make supernatural assumptions, rely on coincidence, use circular logic, or require the individual to possess a supernatural gift of understanding of a divine being. That explanation is that there is no God. It fits all of the evidence, and explains everything in a real way that doesn't require God, Allah, Yahweh, Odin, Vishnu, Zeus, Osiris, Damballah, Gandalf (Gandalf is of course one of the Maiar) or Eru Iluvatar to intervene.
There are certainly things that science can not yet explain, yet it has helped us gain more understanding of the world and contributed more achievements to the human civilization that Religion can ever hope to. A lot of things will likely be known to us, some day, that are not known now. We may never be able to understand everything before the human race perishes in the natural cycle of the universe, but that does not mean we should assign divine qualities to the unknown. It means we need to do more exploring.