I see she did suffer from mental illness, in this particular case I would argue it was more down to mental instability than faith. Perhaps it was thinking that God spoke to her that allowed her to justify it to herself, *shrugs* but we don't know for certain. Whilst I would not place the blame on religion for this particular incident, there are incidents like this where I would. Unfortunately there are teachings in the bible (whether you believe they're applicable or not) that lead people onto do cruel and sick things, even in modern society.
However, as far as mental instability goes, I think religion can have a part to play in it, I'm not suggesting that it was a direct cause to this particular case, but I am highlighting it as a possibility. I think Astreja hits the nail on the head, we are talking about a psychologically abusive God. In some sects of Christianity people are encouraged to repress certain emotions and thoughts and to fear God and what he can do. Some go as far as putting people into a guilt trip for being natural born sinners, like with some Pentecostal Churches. These kinds of things, particularly the repression, can lead to mental illness. So, I don't think it's a stretch of the imagination to suspect religion, but of course, we don't know the exact cause.