She may not be done. I had a snake give birth to 1... and then 48 hours later, 14 more.

Are you talking about a live mouse? I wouldn't put a live one in. A dead one would be ok but if she won't eat it there's no point in leaving it there.

Stillborn babies are not uncommon. I don't think anyone knows why it happens so often, but some are just not fully developed. The ones that need help getting out of the sac usually don't survive anyway; it's their first test of strength.

Realistically, there's not much that can be done to help the weak ones. Move the healthy babies somewhere safe that they can't escape from and give a little water (not enough that they could fall into and drown; it happens). Start them on cut up pieces of fish or nightcrawler but monitor for food fights. It may take a week or two to get them all eating and that's pretty normal.

There's a care sheet around here somewhere that gives a good overview.