Congratulations on the coming baby. I hope you are watching your health (including stress), getting fresh air and exercise, and eating right. Ignore she-bitch, she's jealous and trying to get a foothold in your life, now that you finally have a life worth looking forward to.
So...I typed this out, because I was so angry on your behalf, I just kind of flipped. I have abusive relatives and one is STILL trying to get me to chat with them, even twenty five years of getting away from them, to even more abusive relatives...yeah, so ain't happening, I don't need my kids to see this shit. So, if you're really sensitive like your mom says, you probably don't need to read any further, because I kind of blasted your mom in this.
Let me get this straight. Your mother has stated that she intends to abuse your child, and that she will abuse you and in front of the child, and teach your child that you and your husband are not worthy of respect.
Tell her what you just typed. Actually, don't tell her a fucking thing. Basically you have two choices.
Allow yourself and your husband to be abused in front of your future child, and watch child grow up learning to disrespect you both and talk to you both like shit. Teaching your child to be superficial, and that they should judge people solely on a flawed appearance scale, in which they will always be best, even when they have to make shit up about other people to achieve that fake rank. And that no matter how you treat people, it's ok as long as you get what you want, you can just say people are too sensitive... Oh, and best of all, if they are made the SG, they can come back in twenty years and ask you why you didn't protect them from Ngrandma? Why did you love and abusive grandparent more than them, when your ONE JOB was to protect them?
Send a certified letter to the bitch, stating that under NO circumstances is she allowed to contact you in any way shape or form, under threat of legal action, and if she dies or is in any way depended on life saving apparatus decisions, your responses will be to bury her in a pauper's grave as she is disowned, and to pull the plug, as she is disowned. That as she is currently disowned, you refuse to incur any medical bills or responsibility for her poor life choices, such as growing old. (Yes I am aware growing old is a natural life progression, so is gaining weight when pregnant.)
Right now, you are at a crossroads, and I believe that's what led you here. Yes it's hard to make these decisions, but it really isn't a decision. You have a child coming. Your sole purpose right now is to protect that child, if you value it.
You don't say anything about your husband, what does he say about the abuse your mother heaps out? He cannot possibly approve of this poisonous bitch being allowed to see his child.