The whys and wherefores of what she has don and is doing are irrelevant. What I read in the OP is a daughter who discovered that bad behaviour paid.If she was obstreperous enough, you were prepared to giver her money or look after her children, just to get her off your backs.
I have every sympathy for you, a difficult and troublesome adult child can make life, very difficult for parents who are not naturally combatative themselves.
Unfortunately, often standing up to them is the lesser of 2 evils, because otherwise they think they can order you around, demand money and expect you to be at their beck and call, and when you call it a day and shut up the shop, what follows can be very unpleasant.
As others say, you now need to put your foot down, draw a line in the sand. Tell her that you are now too old to offer her any assistance of any kind with the new baby. She is on her own and has to manage. there will be lots of roaring and shouting and hateful accusations about lack of love and care, she will try to emotionally blackmail with offers and withdrawals of access, but you need to stay firm and just keep saying 'no' to every request.
She is 45, if her life is a mess, only she has made it that way and she needs to learn to live with the consequences.