@kkaida I know this is a really late reponse, but talk to her. She needs someone to talk to. And don't refer to her as Poison Ivy the first time you see her. Of course I love the name Poison Ivy! I'm poisonous inside, and it's a really old nickname.
If you see her being bullied in the hall, help her. (Help her is italicized btw) She needs it.
Don't be too intimidating or the bullies will turn on you, and some unwanted violence will start. Just try to be around her. That's all someone who is depressed/bullied/hurt needs. They want to feel needed.