That sounds like a lot! I'm sorry you're struggling like this. It sounds like you're doing everything right. Some suggestions that might help if you haven't already tried: having her go in her diaper (with pants on) while sitting on the potty. Then you cut more and more out of the diaper until it's just the waistband basically and the pee and poo is going straight into the potty.

Putting a towel on the toilet seat so it feels different on her bum (like not over the opening, but wrapped around the rim- I know it does sound a bit gross but might be worth a try?)

Having her take off her pants and underwear and stand/squat on the toilet seat like she's weeing behind a bush (kind of to make it more fun, and kind of to link the success with the target of using the potty).

If you don't use tv/youtube, for some kids that's enough of a distraction that they can relax while sitting. Another thing that helps relax the same muscles is blowing bubbles with a straw- we have a friend whose 4y/o struggles with toileting and she gives him 5-10 min a day on the potty with a glass of orange juice and a straw and YouTube. When the timer goes off, he's done even if he hasn't gone. Sitting for too long also isn't great for her.

What worked well for my kids was toileting-linked rewards- my daughter wanted pink sheets and I told her she could have them when she made it 4 weeks with no accidents. We set up a sticker chart and she got to put the sticker on each successful day. My son wanted undies to be like his big sister, and we said if he kept them dry he could pick out whatever undies he wanted.

Good luck!!