Have you tried Epsom salt soaks and after soaking using clear iodine? It could very well be bumble but most bumble I've seen get a blk scab over it. You soak in the ES then dry and put the colorless iodine over the bumble then keep them on clean surface do this again in 3-5 days soon you can start peeling the scab off gently and only if it's easy to do you don't want to pull fresh skin off with the scab and make a worse opening. Then once the scab is off clean out the bumble with sterile tweezers you pack with antibiotic ointment do not wrap makes sure to again keep her on clean bedding once hole closes up she can be with rest of the flock. Make sure antibiotic ointment doesn't have pain relief in it.