Not telling her any more news is a no-brainer: she has proven herself absolutely untrustworthy. She should be the last to know of any further news during or after your pregnancy. She has earned that position quite well. I wouldn't feed her false information--you want to take the moral high ground whenever possible--but by keeping her as out of the loop as she has ensured she'll have to be, she will find out the baby's name/hospital/nursery colours/gender/etc. from other people rather than from you. That will get the point across very well.
If she asks why she was the last to find out, or if she requests information directly, work out a stock response that you can use. "Sorry, mum. You made it clear that you can't be trusted with information, so even though we wanted to tell you, we couldn't." End of discussion--she'll argue and lament and say how unfair you're being by 'overreacting'. Just keep repeating this phrase or leave the room. Put it on her for a change.
It wouldn't be wrong for you to say, "Mom, since you couldn't follow our request to keep the news quiet from *everyone*, we are now going to have to keep information from you. And we'll have to watch very carefully to see if you are going to follow our instructions about baby care as well--you'll need to show us that you will actually listen to what we want. I'm sad--I had hoped to be able to be unguarded with you, but it's clear we will need to be more careful."
It sucks for you--I'm sorry this happened to you.
This absolutely. She blatantly went against your explicit requests without remorse. She still doesn't think she did anything wrong, which is a sure
indication that she will do the same thing again if given the chance. I would be very wary of her after the baby is born. Until she earns your trust back, she can't be trusted with unsupervised time with the baby, because there is a pretty huge chance that she'll do what she sees is best, even if it's something you've told her not to do. "Oh don't be silly, whisky helps babies sleep!" or whatever horrible situation you want to come home to after she's been babysitting or whatever. After the birth itself, ensure that while she's around, you have your husband or another pair of trusted and able hands, because you might be too worn out, and there sadly is a chance that she'll try something. "I'll just take little <baby> to see grandpa outside--we'll be back in a moment, stop protesting. Bye!" It will only get worse after the baby is born, experience says.
And I'm sorry this has happened to you. What an awful position to be in: being unable to tell your own mother anything sensitive or quiet.