Unless you have dealt with a friend/family member who had issues like this you really can't understand what goes on with someone with "issues".
I feel sorry for her entire family. The girl had problems and I believe all of the crap she had shoved her way was "the final straw". Obviously I can't say for sure but if she did what she did over this - I think it was only a matter of time before something would have pushed her over the edge. If not this - something would have come along in the not too distant future and cause this same thing to happen.
Such a shame but not all that shocking if you have dealt with people who have "mental health" issues