J.K.
I used to assist in self-defense classes for women and children. One of the most valuable skills you can teach your child is verbal self-defense. You do this by practicing scenarios and giving her the words to use to defend herself. You pretend to be the girl on the bus, the bully at school, etc. If she practices her responses then she has them ready for the next situation. It really does work. For bullies at school, we just taught the kids to say "see ya later!" and walk away. On the bus, maybe "oh, I can't eat it now, it's still frozen" or "no, it's for later" or "you wouldn't like this food; it's Hungarian" or, in response to her friend saying "friends share" she could say "let's share your snack box." She could also ask her friend why she's so hungry in the morning and why she wants her food when the school gives them breakfast. Anyway, some suggestions to start the brainstorming of responses to have her practice.
On a side note, this approach is also useful to teach her how to respond if adults are acting inappropriately or, when she's older, how to handle pushy dates. I am also a huge advocate for women learning self-defense, so I would recommend finding a KidPower class in your area if you can. I also second the suggestion to get her into martial arts for confidence and coordination, and for finding other friends.