What to do about her..

I have this friend, she is suppose to be one of my best friends, and she straight up treats me like crap. She takes our friendship for granted BIG time. She doesnt have the best life so I stick with her because I know that one day she will need me, and loosing my friendship would really devastate her. We’ve been through a lot of stuff together and share a lot of the same friends, so we kind of depend on each other. But she does things like cancels our plans when she is hanging out with guys she likes, but her other friends can still hang out with her, and since her parents like me and trust me soo well she constantly tells them she is with me and goes other places. I’m okay with that, but she does it entirely too much. It’s getting to the point where I don’t think I can stick with her much longer.. I really don’t know what to do.