Do you think this girl is evil?

So theres this really quiet girl in my high school and ive been in most classes with her since elementary and i have never heard her voice. People think she did something bad and take this chance to tease her and when she gets mad she bites hard enough to make you bleed. Because of this she got the nickname Lone Wolf and i feel bad for her. The whole time since ive known her she never seemed to have any friends and when people did befriend her theyd betray her. But besides that shes helpful she helps people before they get hurt like there was this one case where she saved a girl from falling out a window and she saves kids from bullies. She seems to be attached to animals to theres this german shepherd i see that walks her to school and back. So do you really think this girl is bad?