I would get guidance from the staff. Do they have a social worker that knows her? We were advised to use therapeutic lies, but it was advice from people who knew our mom well enough to know what might help. Often you cannot reason with them the way you could before dementia and they often don't have the awareness that they have dementia.
We had to say things like "Sorry mom, they are painting your house and removing old carpeting, it will be another few weeks." "They found x,y,z bugs and are fumigating. You can't inhale those fumes."Reasoning with her made her angry, but having a made up reason why she could not return right now with the hope it was temporary calmed her. She did not have the cognitive capacity to say "hey, it's been a month, aren't they done?" She just needed up to pretend she was fine and there was a reason other than her aging for her to be at this place.