I'm sorry for your loss. It's a heartbreaking thing. It sounds like your mother has had a missed miscarriage, where the baby has passed away, but the pregnancy stayed in place. I had one at 11 weeks. They told me the baby had passed two weeks earlier. :(
One thing that really helped me was to find online support. I know that sounds weird, but it helped to be able to let all my feelings out to people who understood, but not have to do it in person, because every time I tried to talk about it out loud I'd choke up crying.
The forum I found support on is called Life After Loss, and is based in the UK. The women there are so supportive, and they have all been through the loss of a child, either during pregnancy, at birth or shortly afterward. If your Mom is interested , the site is lifeafterloss.org.uk It's been pretty quiet (most of the ladies are on facebook and now do a lot of their casual chatting there) but the boards are read frequently, and new posts are answered quickly and with overwhelming empathy and support.
I hope that helps. Again, so sorry for your family's loss. :(