How can we pay for Assisted Living?

Our mom had a hip replacement and has severe COPD. She's 89 years old and currently on 24/7 oxygen. Soon she will go through a pulmonary rehab and afterward hopefully only need oxygen during sleep. Now, she's in a board and care home but it's too expensive to keep her there indefinitely, as it seems to be handled only through private pay. She doesn't qualify to be in a nursing home. Her only income source is social security. Our family of 3 does not have funding for this for board and care. We've been using Mom's credit card, thus far. When her health improves through the rehab, and she is deemed to be "free" from the board and care, what can we do? My sister was close to 'burn out' BEFORE her surgery in March! We need financial aid, maybe for Assisted Living. There's NO WAY my sister or I could live with our mother. She's been 'a tick off' mentally her entire life!!