pecking and bald patches

One of my chickens has always been a bit more scruffy than the others and been a bit featherless at the base of her back and another patch just above her tail feathers.  However, the patch on her back is now much larger and more red and the two other hens appear to be pecking her more.  Can I do something or spray something on to stop the others pecking at her?

Also I noticed today on the patch just above her tail feathers that there was something like a raised cyst like a large mole but light in colour.  I wondered if it was perhaps an ingrowing feather.  Is there something I can do about this too?  I didn't want to try lancing it in case it caused an infection or some bleeding which I thought might cause the others to peck her more.

I am reticent to separate her as I think when I re-introduce her it would cause more bullying.

Any help anyone can offer would be much appreciated.

Yes, the "raised cyst" will be the preen gland which secretes a special oil that the birds use with they groom themselves.

Feather pecking can become a very bad habit, and I would probably try break bits (you can buy them from the domestic fowl trust).  the bits prevent the beak from closing enough to grip feathers, but don't stop the birds from eating or drinking.  usually they can be removed after  a month or two.

For the moment, I would try purple spray on the pecks chickens back.  This will help to disguise the redness of the bare skin.  You could also try increasing the protein in the diet for a while.  As sometimes feather pecking can start by a nutritional deficiency (usually protein and/or biotin).

To increase protein, you can supplement some the layers pellets with an unmedicated turkey or phesant/quail starter, or add crushed soy beans.