Ethel she is just mentally torturing you and it's not on. You do your best for her, but her demands just keep coming and nasty remarks with it so walk out when she starts, don't take it. I would wear music buds in my ears and go about ignoring her.
My uncle was in a care home and my mum and I visited him 3 times a week. It wasn't enough, we didn't care, we took his money( we couldn't and wouldn't) etc. The nurse told us to stay away for 3 weeks, let him stew, which we did. Every time he went back to his old ways we did it again.
Please look after yourself, you need time for you. If you can afford to, book a weekend away to recharge your batteries, I know your car getting fixed is a priority though. I hope 2023 will be better for you, you need a bit of happiness in your life.