I am so sorry to hear about your DP. 
I can imagine how hard it is to think of doing this on your own. But honestly, it will be much harder with toxic people in your life.
I do not say this lightly: I know first hand as I've raised my two children alone since they were both babies. It is relentless. But not in a million years would I let my toxic mother into my life to make it "easier". And anyway, you know that it won't. It can't.
For me, the reason I cut contact with her was because I was planning children with my now ex-H, and while I'd tolerated a lot of awful treatment to me - and I mean really awful abusive behaviour here - I could not contemplate letting her near my own children without her acknowledging and addressing it. I tried to talk to her. She stood up and walked away and then sent me a letter saying I was a liar. When she knew what happened, she was complicit in it all.
These people will never change. I cut contact then and although it is hard with two kids and no family support and no partner, it is doable. I have a full time job, I have bought us a house, both of my children have additional needs and I'm disabled myself but we manage to support ourselves. I feel stronger now that ever. It can be done. The idea of letting my toxic mother near my children is not something I would contemplate. It is not a solution, it is not help, it would be harmful to us all.
Try to focus on what you need to do now. It sounds like you have been through a great deal and have yet more trauma happening now, on top of pregnancy. Have you spoken to the perinatal health team? Please do - they are usually very supportive. Ask for trauma therapy, you can work through this. It will be hard but it is much, much healthier to do it alone than to have toxic people in your life. They always make things worse, you know this in your heart.