Mom is making terrible financial decisions BUT won’t listen to advice that I’m giving and feels she’s doing absolutely nothing wrong.

See if the following is possible. Tell mother that the Bank is opening new accounts (because of hacking?). Set up a debit card attached to the new account, and a new cheque book. Keep the new account topped up to about $500. If it works, it does limit the exposure. You can always say that you are having trouble getting it straight, if things bounce.

She can no longer reason or process what it being explained.

Like what?

Depending on what sort of decisions, maybe there'll be other ways round the problem besides getting her to agree with you.

You can tell Mom you want to “help” her. Tell her you’d like to learn about her bills and other expenses and will she show you and “teach” you how to do it. Ask her how she records her expenses, where she keeps her receipts, etc. Then, at the right time, tell her you’d like to do it for her so she can do “some fun stuff” and not have to worry about “all this other stuff”. Keep trying until she’s on board with it.

Time is of the essence. Seniors are vulnerable to scams. The mistakes she’s making now can have long-range effects and could take you a very long time to fix. And like Barb says, make sure someone has a power of Attorney.

You can't get someone with Dementia to "listen" to you--you are trying to reason with her and her ability to reason has left the building.

Her brain is broken.

Do you have Power of Attorney for her financial affairs? Read it and see what it says.