You are starting to see clearly at last and are breaking a cycle of behaviour that may have been going on in your family for generations.
Your mother taught you that any marriage, no matter how crap and abusive, is better than no marriage. Children can be sacrificed for that marriage. All that matters is the outward appearance and material comfort. You learned that because it was how her marriage was, and how you were treated.
She probably learned that from her parents marriage. And her mother, from her mothers marriage. Which is no excuse at all, by the way, maybe just an explanation. They weren't as strong as you. She's so resistant because frankly you are showing up how wrong/weak she was. She knows it isn't right to lock a teenager in the bedroom to prevent her stepfather raping her. She can't face what she did. She has to stick to her script of putting up with anything for appearances sake.
You are the one to break the mould and say 'no! this is NOT right'. Which makes you pretty fucking amazing, actually, and brilliant not to be now sacrificing your own children in favour of an abusive man, and teaching them the same lesson.
You know she's talking utter codswallop about your future. What your house is like, what your furniture is like, how much money you have, doesn't mean shit at the end of the day. (and if that sounds trite, believe me, I've lived in absolute shitholes and been skint and wondered what I was doing to my son, but it didn't matter), What matters is how happy you are. And you and your daughters are already much happier.
I suppose how you deal with it now is down to how you can take her attitude. If you feel pity for her for being so weak and misguided, and for harming you both as a child and now, perhaps you can continue with contact, at your level of comfort. If you feel just anger at her for being so weak and misguided, and for harming you both as a child and now, then go no contact. No one can make that decision for you and no one should judge you for whatever decision you make. She hasn't been much of a mother to you. You don't owe her anything. The point is whether she can ever offer you anything. If you decide to keep contact, you'll probably have to talk all this through for her. If she were willing to go to some sort of family counselling with you, that would help. If she isn't willing to do anything towards your relationship, I suppose that's an answer for you.
As an immediate thing though, flag her email account as spam, and stop even reading the garbage she is sending.