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 when fiddled with ? If not I am tempted to say leave it be and keep a close eye on it. But carry on the warm baths.
If the scab can be removed and it looks like a bumble you are probably going to have to cull as it’s so close to her heart and operating is impossible in my opinion.
If it’s not a bumble ?

Update after new photos, hell ! I’d bath and try to debride then put on antibiotics with a strong cream and a dressing. No walking either and feed high protein. Poor love.
If you can’t debride I’d cull

Hugz