At 40 pounds it is most likely the ankle and knees giving out. I have seen it on some of the BB’s I raised. It looks like bumble foot but it’s just the joints deteriorating.
I would avoid any antibiotics, unless you won’t eat her under any circumstance.
I won't eat her, she's just a pet.
Darn, I was expecting she wouldn't live long, but I was kind of hoping she'd just peacefully die at some point. Maybe I can get her some anti-inflammatories.