What happens to an elderly person transferred from the hospital to a rehab center and loses her home in the interim?

Sounds like someone will have to either take her in or she will have to go to a nursing home, senior center, etc. I don't know how old this "elderly person" is, but hopefully her sister wasn't the only one watching out for her? We need a little more information to give decent advice, but whoever is her "caregiver" should be checking with the social worker at the rehab center - and fast.