Oh, that's lame Stephie. Just tell them you're not going to the cabin until much later. If there's a music fest your mom should be ok for a few hours, right? I'm confused how she even got there if she has no way home. My therapist says that as an adult you have to detach yourself from your immediate family in order to form your own. Your family will resist this, and become angry if you don't perform your expected role, but you have to do it. So I urge you to stop cancelling plans for things your family just expects you to do.
But in the short term, if I have D and I'm in and out of the bathroom, I'm not going ANYWHERE.
Hang in there, take it easy, and take care of yourself.