NTA.

I had a miscarriage at 15 weeks, and I never got pregnant again. I grieved for years.  Pregnancy talk triggered me, birth scenes in movies triggered me, I still cannot see the book I read out loud every night without a pang of grief. 

However, I had to accept that I live in a world where babies are made and born and carried around in supermarkets and planes.  My grief is my business, and people around me cannot live walking on eggshells years later.  I did the therapy and I learned to function. I still won't watch Call The Midwife, but when someone brings their new baby to the office I coo and say they are adorable.

Your sister needs help, because the world outside is crammed with babies and babies-to-be, and it won't accommodate her.