Is there a short term hospital of sorts for a person with dementia?

That Medicare will pay for until a person is moved to assisted living. Mom seems to have turned a corner this week and her dementia has become five times worse, all of a sudden. Part of it is, if her regular routine is altered at all she zones out and gets upset and confused. The Christmas holidays have thrown her for a loop even though we did everything for her. We included her in the family holiday activities, but she couldn't seem to figure out what was going on, or care. Christmas she sat and didn't speak, and even minute by minute she seemed completely uninterested in opening her presents, yet she did eat some dinner. She didn't recognize several people she has known for 30 years. She seemed confused half the time then she would act normal for a while. She started having a problem walking recently, but at 100, is that surprising? She's mostly deaf, but even if she hears us, she doesn't really get what we are saying or remember it two minutes later because she isn't comprehending.
She is a loner, always has been and so far is capable of getting herself up and dressed, going to meals, taking care of her personal needs, so the doctor thinks she would do ok in assisted living with guidance and some oversight.

Is there some sort of short term hospitalization medicare and insurance will cover if the IL facility notices she is worse and calls and says we have to move her NOW? They have been patient about it for a couple of months while we wait for a room at AL which will be within the next month or so. But what do we do in the interim if she can't stay there for a few more weeks. She won't let an aide in the door, my sibling can't help, so I'm feeling alone and worried.