Other question - was she an only child? Siblings tend to stick up for each other which lessens the effect.
And where were her friends? While she was a loner, when i was in school EVERYBODY had some sort of clique.
Also, it is strange that the switched schools twice and had the same experience at all three schools. Maybe her story followed her around or maybe she was just the type who attracted this sort of behaviour. NOT sticking up for the assholes but we all have met people who just can't get away from drama and issues.
kids at that age (and pretty much any age) will usually take off when things start getting ugly. one by one they start disappearing. sadly, i've done it myself...abandoned people who were once friends because i had a choice to be "friends" with more popular kids but it took me not wanting to sit with "that guy". you walk away and aside from a couple minutes every once and a while of feeling bad or maybe even guilty, you enjoy being with a better class of loser. people are always willing to move ahead at the expense of people getting left behind.
with all that baggage that followed her and the lack of self confidence and self injury (that kids all know about quickly), she essentially becomes unfriendable (if that's a word). the cuts on her arm becomes a scarlet letter that screams to people "stay away!"
it's not hard to imagine that this girl had little to no friends.
i think you are right that she and others just attract this kind of drama. it's wierd. bullies, abusers, and manipulators can sniff out weaker people and learn from an early age how to take advantage of the situation. meanwhile, there is a certain amount of naiveness and gulibility with those who keep falling into these situations in that despite how ugly hey have seen tha tthe world can be, there's this hopefulness that maybe..just maybe this time this person really might like them and they want to believe it so bad they just open themselves up to it.
good kids are told from an early age to keep to themselves. they hear from their parents that it's better to just not get involved and so those who could probably help the hurting kid are usually trying to keep their distance. they think what their parents think...that "it's not my place". meanwhile the bad kids are a lot more bold and are looking for the next conquest.