What should i do? concert.?

Well i guess you could come up with a little white lie and say that someone in your family is sick and now you will not be going and since you are not going then the rest of them have bailed out also. I mean, it sounds like you really wish she was not your friend and that she is just a tag a long. And yea that can drag down the fun. I suppose either use the lie or just tell her we are going to go upfront so you can do what makes you comfortable , if you want to you can stay in the back with my mother but it is up to you.