Why does she only have one bank account with "ALL" her money in it? That's nonsensical. It's akin to her walking around with all her money in cash in her handbag. Get a different account for her to use as "spending money" and get her to keep the "main" account card safe at home. I thought everyone did that?
We even did it with our DS when he went to Uni - he's now got 2 bank accounts, one with his savings and where his student loans and wages are paid into (the card never leaves home), and a Monzo account for spending money that he takes out with him (and is on his phone). He set up a standing order from his main account of £x per month, which not only protects the money in his main account but also acts as a budgeting tool as he can only spend his monthly transfer sum, which is the maximum he can "lose" if the card gets stolen or cloned or he gets drunk and goes on a spending spree (never happened).
Just done the same with mother in law who has dementia. She had a weird convoluted "system" of several bank/savings accounts with passbooks etc and would spend a full morning every 2 or 3 weeks going to one bank to withdraw a shedload of cash, traipse across town to other banks to pay it in, pay some bills out of one account, other bills out of another - heaven knows why she made it so complicated - she can't even remember why she had so many accounts and didn't really understand what she was doing - she just did the same thing out of "muscle memory" rather than anything else. She "lost" huge amounts of cash and she'd hadn't a clue where it went. Not one offs, but just "dripping away" every week. She'd withdraw a few hundred in cash, and it would disappear - she'd not go anywhere or do anything, but a week later, she'd only have a fiver in her purse. The thing was, she was so paranoid about losing money or having it stolen, she'd hide it - on occasion we've found some in socks in a drawer, in a pillowcase on the bed, in a cornflakes box, so we assume she'd accidently throw it away (with the rubbish if in a box or tin) or it would disintegrate in the washer!
OH took control after he looked at her passbooks to work out how it all "worked" and realised that thousands were disappearing over a year (he traced between bank accounts, logged her household bills, etc), and there was a huge black hole of untraceable cash, withdrawn from one account, but disappearing before other bank account pay ins and bills. We knew cash was going missing but the sheer size of the loss was shocking. Over a few weeks, he got her to close all the passbook accounts and just kept 2 card accounts, with different banks. He then got her pensions paid into one account, and all her direct debits paid out of it, so that became her "main" account, then the other account was her "cash" or spending money account and he set up a standing order. She now goes out with her "spending money" card to do her shopping and we take her to the cash machine to withdraw cash for birthday presents and a tiny amount of cash for the milkman and window cleaner. The "leakage" has stopped virtually instantly - she's a lot happier as she finds it a novelty to "touch" her contactless card to pay for things - yes she's written down her pin number for when it asks (is it after 10 contactless?) but there's so little in the account, it's not the end of the World if the card got lost/stolen and used (losses would be massively less than her previous cash leakages!). She's in her 80s with dementia and just needed someone (OH) to take control and show her how to rationalise her banking/cash use and streamline it to be safer and simpler! We were talking over Xmas, and she can't even remember traipsing around between banks nor even using cash to go shopping - using her card is now all she knows!