If she were mine i would wash it really good and my dad said put peroxide on it one or two times a day. And probably put some antibiotics ointment on it thats all we can think of. And it might not hurt to take her to the vet. How long has it been like it?
That's staff infection and needs care to save that teat. Do Not use ointment on it. Treat inside and out.
Today infusion inside after milking out that side and fight bac or chlorhexidine spray outside.
Put a water based udder cream on to ease milking and try not to damage the teat.
Put her kid elsewhere and bring him to nurse the other side while you are milking, he will help her milk out easily.