21 year old cat

Hello, my cat has been generally healthy but over the last two years developed a thyroid issue which has been controlled with medicine. However she is now at the highest dosage amount.

I also believe she may have dementia, she has stopped grooming well over the last few years but I had been able to brush/clean her and keep her long fur decent, until the last few months. Now she gets angry and with her small size it is very difficult to brush her. She is now starting to mat but I’m doing the best I can. Another reason I believe she may have dementia is over the last 2 weeks she has started yowling during the night and acts like she doesn’t know where I am.

I have a vet appointment scheduled soon but I am afraid I know what is coming. Is there anything else I should be trying to do for her to make her comfortable and anything I can do to help her with her night confusions?

Thank you