I think you did the right thing by just walking away instead of getting into it with her! She had no right to say something so rude to you, especially that you've already lost over 20 POUNDS and you have TWIN infants to take care of!!
the fact that she lost a baby, well that is sad and tragic but has nothing at all to do with you.
You keep on doing whatever you are doing, and I hope no one gets in your way!

If you want to avoid family get-togethers, I think that is fine.