Cold girl was right about that you need to communicate with her. However, I will add that though you think yourself to be quite mature.. well, you are still both young and I honestly wouldn't expect much if I were you. It is likely things won't be fixed, and in that case, you need to do what is best for you. Be sensitive, don't do anything too hurtful..but to put off breaking up with her just because you are afraid she will hurt herslef may actually be more damaging. You can only really be responsible for yourself. What she does is her own business. You can't feel responsible for her actions. All the more you can do is try to be kind and caring while also looking out for yourself. What she does after that.. that is up to her.
EDA: However, if you do break up and you are still very much reasonably concerned, don't be afraid to talk to the school or her parents. Even if YOU can't take care of her, someone else can look after her and make sure she's safe.. even if she hates you for it... at least she'll be safe.
Sorry for this.. you seem good

looking for a relationship in which there's actual communication and mutual respect. That's good. But, its my own personal advice if that is what you are looking for.. honestly, maybe wait a two or so years before you start deciding to date again.. when you are older, the girls are older, adn the relationship sare much more likely to be mature, lasting relationship.s