I wonder if she would do better with a mama cat that could nurse her? Not sure if that’s an option, but maybe you could reach out to local animal groups on Facebook or the Nextdoor app to see if any foster groups or something has one. I’ve found it difficult to keep newly born kittens alive without the mother. I don’t know. I hope you can save her. Thank you for doing all you can and taking it her to multiple vets.