Go ahead and be admitted. You don't want to wait until your MG gets to an MG crisis point. It's far harder to recover once that happens. ALL insurance companies make it hard for doctors to approve anything but that does not mean it's impossible. They cannot keep you from a life-saving treatment. There are ways around that, such as being admitted.
Go ahead and let them do it! You need to put your ankle up and rest it anyway.

They will treat it in the hospital as well. I hope you'll be ok.
Annie