Does a person in rehab on Medicare have to be released one day but wait until the next to go back to their assisted living facility?

Medicare does not pay for Assisted Living. The other problem is that the Assisted living place has to re-evaluate her to be sure she is still suitable for their facility. If you are thinking about pulling her out of rehab AMA (against medical orders) you could get stuck with a big bill, then you arrive at the ALF without a re-evaluation and they won't take her back.

This sounds bizarre - do you mean that Medicare will not pay for any days, or just for the day she actually leaves? If she does not complete a full day at facility, then maybe Medicare refuses to pay for that particular day. I'd check with a social worker at the facility to be sure I understood this right.