My mother was my abuser too. Your feelings aren't wrong at all.

You deserve to be treated well.

I was trained to have no boundaries, no self, no ability to say No. But step by step I did say No, take a stand for myself, develop healthy boundaries, and get clear of abuse.

Wherever you are in your healing process, you are fine. You are okay and doing the best you can.

You could call her and say something like "Mom, my plans have changed, I'm not going to be available for a visit Saturday.". Or if need be you could even simply be away during that time, go do something fun for yourself.