Oh dear. We had a very very similar altercation with my in laws a few months ago. After 10 months estrangement (which was mainly us saying 'we wont put ourselves through it anymore) we decided to reach out to them when I was around 18 weeks pregnant, asking them if we could all try to work things out and move on so they could be part of ours & therefore their granchildrens lives, and were met with a less than kind response.
Over a few days, dh basically all but begged them to reconsider but they wouldnt. He eventually told them hed never forgive their lack of effort to be part of the kids lives, and I dont think he will.
Its desperately sad really, as is your situation. But you cant force her and you have to question the decency of the person concerned putting a heavily pregnant woman through this.
All I can say to help is that now, a few months on, my husband and I both feel the most positive re the situation that we've ever felt. We did our best, they didn't, they have to live with that. How they can not want to do everything possible to be involved with their lovely son & grandchild is beyond me and for that I feel disappointment in them, but not sad anymore and not angry, mainly indifference.
I think for you its important to try to let this go for now, although believe me I know thats easier said than done. But you need to think about this special time in your life, you dont want to look back and feel it was overshadowed. Think of your dh, ds and new baby, and enjoy it. Its her loss. Dont waste anymore energy on it for now. If in a few months you still feel you want to repair things, you'll have more emotional capacity to deal with it when baby is older. Hope youre ok x