i do know of something that may help you, it is called "ABC jell", you get it from health food shops, this is fantastic for the growth of new hair from scaring, the reduction of swelling, it is great on most things, even for humans. it is not expensive under $20.00 and has been used for many years. it may take some time to have any affect, so be patient.
I know of a horse the vets said to put down, he had a cancerous growth on his leg, after aplying the "ABC jell" the growth went completely away, the horse is now doing top dressage.
i am into the natural healing of horses.
I do agree that a vet should also take another look at your horse, if only to put you at ease.
hope this helps.