If you do manage to take the crust off the wound please be prepared that she still may not survive as the shock and stress of the event could be too much for her.
I wish I could be with you so I could try to help you through this but I will keep the site open for the next hour so I am here if...
It looks a lot like a very large bumble, but a very odd place for it,
I agree try soaking her in warm water with either Epsom salts or Betadine for about 30 mins (make sure it it totally covered) then see if you can find out if the scab is movable and you can see underneath.
Does it hurt her...