My 83-year-old mother and her husband may need to go into a nursing home. Will she lose her home since his SSI pays the bills?

This will depend on many things, including whether they go on Medicaid, and it sounds like that is likely. It would be a good idea to see an estate attorney about this. If they are both in a nursing home and they use up their assets, there will likely be a lean placed against the house for expenses, but only an attorney can really sort this out for you.
Good luck,
Carol