You're in summer school right now?
Given your age group, and the fact that she's already being bullied, I think it's time to make the school authorities aware of the situation. Some of what you believe may not be the whole truth - not out and out lying, but exaggeration. Furthermore, if there is real abuse, it is a lot better for her if it is the school advocating for her, rather than her friend (you), who is a minor.
And yes, you need to specifically tell the school (you can leave an anonymous note in the office for the school's guidance counselor) because most schools are pretty big, and teachers and principals are overworked. It's not that they don't care; it's that they can often be overwhelmed.
So drop this very, very big hint, and drop it again in a month if things do not improve.