Can an assisted living facility charge for just having a higher BIMS score than before?

I don't see where her cognitive ability has anything to do with her cost of care. And I don't think an RN (if that's who gave the test) has the ability to make decisions on how well the resident did or didn't do. Now if her physical care has become more, thats different. My Moms AL had 4 levels, Mom was #4 so she was paying the highest care level going in.

Private AL facilities can charge whatever they WANT to charge which is certainly 'legal'...read the lease agreement you signed. Your mother is being assessed and charged points for her care plan, which is the same as my parents were being charged in their ALF. The 12 points she's been assessed are going towards her care services each month, and cost X amount of dollars. Ask what score she needs to have to require Memory Care placement/transfer.........that is when her fees will increase dramatically & when she'll have to move.

The BIMS test isn't so 'dumb'; in reality, it tests your mother's cognizance level and determines what level of dementia is at play at any given time. You state in your profile your 91 y/o mother suffers from dementia/ALZ, so you're better off knowing where she stands and when she needs Memory Care vs. waiting for her to go wandering off out the front door of the ALF one day unassisted before you find out!

Good luck!

They are not charging you for the care assessment, but for the care needed and how they are gaging that charge should be fully explained to the POA. Were you there for the testing? Are you aware of the fully test done and all involved, and were you delivered a full explanation by mail (if you are POA) for the changes in charges and the reasons for same.
Care levels were very well defined in my brother's ALF. They were also always open to discussing with the POA any changes in charges, and any changes in care being given.They were very upfront.
Do know that ALF are not regulated in the same way as a Nursing Home and have fewer laws that they are required to obey for the licensure that Nursing homes have to qualify for. They are more or less rentals, but with added amenities such as caregivers to assist with bathing when needed, caregivers to check on people with mentation difficulties more often, medication techs or nurses to deliver medications safely.
Discuss your concerns with your Facility as POA. As to be fully updated. And yes, the jumps in cost between levels I, II, III and IV can be quite shocking. You are nearing memory care costs before you know it. HOWEVER, that said, you will understand when you simply visit a facility the enormous difference in needs between a walking, reasonably competent elder who showers himself, is able to keep his room(s) neat, able to come out for meals communially, dress self, safe to come and go, no incontinence problems, and other residents with more needs. In my brother's case he was able to function independently almost completely. Many of his fellow cottage residents required a lot of care and checking, and to be frank, a few should have been in a higher level of care and were very difficult in the ALF for the aids to fully address needs.
I sure wish you the best. ALF are unique in of themselves. Speak with the one your Mom is a resident of, and feel free to "explore" others in the area, ask for packets and be fully informed of what they may offer.

Was she able to draw the clock and add the correct time? This is also part of the test and gives doctors an idea of their cognitive impairment level (along with the memory test).

Did you ask the facility what specific service they are providing for the extra money? I agree your mom should be getting something for the charge. In my state each resident gets a rating every year. Once more impairment is present, then services like now needs meds administered or "requires 2-person lift" (where they may have been a 1-person lift last year) contributes to the cost of their care.