[sc_rufctr]

Sounds awful but I suggest that you don't cut ties with her. I don't think anyone deserves that unless they've done something truly unforgivable.

What you could do is stick up for yourself and don't let her drag you into her affairs. Just focus on your own family and what's best for them.
If she wants to see her grand kids then she needs to make an effort. Don't play her games. Just get on with your life.
If she starts bad mouthing your dad stop her cold. Just stop her and make sure she knows it's not right for her to do that.
She may not understand at first but eventually she'll get it.

I was lucky with my parents although my mum can be demanding and intrusive at times but she means well.
After my dad passed she had a really hard time adjusting.