Oh no! I hate to hear that. Glitches are striking again. Did you try resetting her?
I've reset a Pregnant Sim in the past and they got stuck like that, I'll try it if it happens again though. I am really depressed about this mainly because, George gained Immortality and I did tonnes of building work like the new Museum and such. There was also about §200,000 worth of Celebrity Gifts in the Family Inventory! I sold them and got them all cars. I also really loved the nursery I made. I was about to have Gen 4 turn into a Toddler when I decided to quit because Mag had not given birth.
Off I go again then, to try and fix this stupid thing.