It'd be a little bit odd for her symptoms to be due to dementia given her age and the sudden change in her mental status. More likely it's related to her mental illness. There is such a term as the 'kindling effect' which basically says each bipolar episode gets more severe and lasts a longer period of time. There of course is debate about this but it's becoming more universally accepted. That being said, based on the info you typed about your mom, I would be shocked if her mental status is due to dementia (and there really isn't any imaging that would be tremendously helpful to tell). Typically in these cases, they try to make the patient better and see what the person is like after they're under better control. At that point it may become clear whether it's dementia vs. mental illness (or both).

Maybe you could talk to your mom's social worker in the hospital and set up a family meeting to discuss her treatment with the whole treatment team (social worker, nurse, doctor). They would be your best bet to figure out what needs to be done, like the others have suggested.

Good luck with this situation. Hopefully your mom will show some improement shortly. Hang in there!