Advice on friendship problem?

I have this really bad tempered friend. She and her bratty friends have been mistreating me lately, talking about me behind her back and leaving me and running away from me. She was bullied in 2nd grade, like 5 years ago. I'm in 7th grade now, and she has been a pain. She knows i had depression problems and people were mean to me in elementary school. in 6th grade that problem cleared up a bit. But Friday, they were gossiping about me and planning to ditch me again, so i got really mad and ran away before they could. I called her a brat, and she got really mad. she is acting so immature. What should i do?!