this is disgusting!
No way should he be changing his will. He pays her the 'going rate', and that's all she's frigging entitled to.
Blow her up to the tax office, because I doubt she's paying tax.
I've worked in health and social care for years, and there is no way on earth I'd be expecting this kind of 'bonus'. In my last job, I wasn't allowed to even except gifts unless they were under £5, say, a box of chocs at Xmas, and I and my manager had to sign a book to say I'd received something.
adult safeguarding, social services, would be my first call. I'd also make damn sure that any high value items in the home, such as antiques or jewellery, was removed as soon as possible.
I'd also make sure that he's not getting scammed in other ways: gardening, cleaning, fixing the roof: these scumbags usually have a little group of scammers around them who all milk the old person until there's nothing left.
I'd also make sure his medication is okay. It's pretty easy to obtain sedative drugs, for example, and administer them to the 'cared for' without their knowledge, and that makes them more compliant. Also increases their risk of falls and risk of self neglect.
I'm not saying she's a wrong 'un, but, if she is, then your Dad could actually be in serious danger.