Its not unreasonable for her to DESIRE to spend it with you since you can't travel with your family. But she needs to be respectful of your wishes for low stress since you are pregnant.
If your hubby is not comfortable telling her no, just call her yourself and tell her that you don't want to make any plans or have anyone over because of your due date. If she argues with you just tell her that mommy hormones are making you stressed out and it would be too much. If she still doesn't want to give in change the conversation and insist your hubby tell her to back off. Men don't like to rock the boat with their families, I am sure he doesn't want to bring it up. If its a simple thing with their family, we should be able to handle it. If its complex then its hubby's job since its his family.
Honestly you might have a newborn already, be in labor, etc... so it could be a non issue. But straight forward communication is always best.
I had to do something like this once with my grandmother. We lived close one year and my in-laws were coming. I called to invite my grandma to our house and somehow in the conversation she got the idea we were coming to HER house and that we would make one of her favorite meals instead of the traditional Christmas dinner I had planned (and asked several people to make food for already). It was really awkward and I had to call her back later and explain that we were not coming to her or eating that food, it was a misunderstanding, and that she would come to us... ULGH! it went better then I was afraid of and everything worked out fine.
Best wishes!