Dealing with a Narcissistic Abusive Parent Caring for Your Child

How do you deal with cutting off your narcissistic abusive parent who is caring for your child? my son and I are temporarily separated because I had to leave the town I was in, but I didn't want to take him out of yet another school after just starting last year. My mother is wonderful with him, but has always been emotionally abusive to me. I want to proceed with no contact, but I don't want to ruin their relationship when he can finally join me in our new home. She is dropping him off for a visit tomorrow, and I know she is going to try and force me to talk to her. I don't know if I'll be able to keep my composure.