Straw is fine.
I was more concerned about their run area. Basing off from your profile picture there run area is mostly compiled of hard compacted dirt which offers very little cushioning, to their footpads and feet which may have been a partial cause of the Bumblefoot. Filling the area with...
That's good. Keep on doing so until the core is fairly loose, then try taking it out. Ensuring their bedding substrate is soft, clean, and free of hard objects will ultimately help prevent Bumblefoot from occurring in the future.
Sorry, I didn't see your reply.
She definitely has Bumblefoot. If she were mine, I would start soaking her leg in Epsom salt water for a few days, to loosen the core, then try to take the core out with a scalpel, and tweezers. If there is bleeding when you are taking the core out, apply firm...