My friend was recently moved to a smaller room with a shared bathroom across the hall to accommodate a man who took her room. This is a small place and the owner said the man was required by law to have a private bathroom. When she moved there, she was the only resident and the owner told her she could have whatever room she wanted. She settled in and was doing well. There are only 3 or 4 rooms available but the one she was in had a private bath. None of the others do. The only other resident there is bedridden so needs no access to a bathroom. I think the owner got more money for the private room with bath but I think it's unfair to my friend.
If someone has certain contagious diseases, then yes, there are laws that govern if they need a private bathroom.
My dad was in a top facility and he had a shared bathroom, it's not really that uncommon in facilities. Then he moved to a board and care and the house only had 2 bathrooms. What a nightmare that was but, everyone worked around it and those that couldn't hold it, had bedside commodes.
Your friend is paying rent for the room. If her rent includes a private bath and she no longer has one, then the price of her room should come down. Another thing is her lease. Does it run from year to year? If so he may have prematurely moved her out. He changed the rules so he cannot keep her to the lease. Has she changed over to Medicaid recently. That could be why the room change.
IMO, an AL is a residence with a lease in place. As long as you are paying for that room, you cannot be asked to change rooms. Just like an apartment. I personally think that he was able to do this because there's no family close by.
I would assume daughter pays Moms bills. She needs to make sure Mom is not being charged the same price as of the day she was moved.