I am never one to terminate just because a parent is annoying. The grass isn't always greener. In your case I would be very firm with mom. Tell her this is the way it is end of story. Have you been somewhat flexible and that's why she thinks things can be?

I would be letting them know that you have a family interested in full time and offer her the spot full time. If she says no then goodbye.

Also do not open on a stat for her! This is what makes me think you have been somewhat lenient.

There is no guarantee with the next family and I don't believe in terminating just because we don't like someone we chose. She is just testing her boundaries and once you show her who is boss things will get better or she will leave.