My live-in-the-basement MIL has mild dementia,

[Binkie The Clown]

12. My mom with dementia lived with me for 6 years.

Little by little her memory loss got worse, but then, last year, she stared getting noticeably worse week by week. While she was still somewhat coherent my sister and and I went with her to the bank and had our names added to her accounts so that I could take care of her finances, and my sister could act as backup in case anything happened to me. We went into her purse and removed her car keys and credit cards. That turned out not be be an issue since she hadn't driven for more than 3 years and never went shopping by herself, since I was her only source of transportation.

We were glad that we went to the bank while she was still coherent enough to talk with the bank manager and to agree to add us to her accounts. If we had waited any longer, given how her mental faculties deteriorated, we probably would have needed to go through the courts to get our signatures added.

As it was, we were cutting it close. A few months later her doctor recommended her for hospice and five months after that, she passed away. Having our names on the accounts made settling up her finances and splitting up the assets with the heirs much easier.

If she can still carry on a halfway reasonable conversation, I would strongly advise going with her to the bank and getting your names and signatures added. The longer you wait, the more difficult it could become. Emphasize, like we did, that we wanted to help her with her bills. Don't make it sound to her like you are trying to "take over". Just offer to help.