Secondly, is your mother diagnosed and in medication/it’s being managed? Because this doesn’t sound like her BPD is going so well right now, and if there is someone who could help her see the light- her dr, your father, a sibling, etc reach out to them. Depending on what you want, which wasn’t clear but I think you want your mother around and for her to cut the shit with your MIL and now your husband and soon to be child.
You should write this all down, or show her this post or something and try to have one last come to Jesus. This is not a competition, but if it is and she decides to spoil everything by not showing up and missing out in her grandchild’s life because of her feelings and perspective of what is happening is not your fault.
If your mother is undiagnosed and none of the above is possible, I am sorry. But you deserve a mother who loves you instead of one that fights off anyone close to you. That she would call your husband and unborn child rude is at the point where I think she needs help, therapy, a dr, someone to help her into better treatment. And that really shouldn’t be you, because you’re pregnant and you don’t need the stress.
Are you seeing a therapist? You may want to. My mother is not diagnosed but I’m fairly certain (I’m not a dr but I did take courses in psychology in college) that she is BPD and she behaves like this and will isolate herself from everyone who she perceives has personal slighted her. The best hint I did (after I became a parent) was to see a therapist about my own childhood.
Good luck, protect yourself and your child, sadly even from your mother if you need to.