I think your poor little chicken has Endophthalmitis. This is swelling of the globe, with about 3 causes.
One is penetration of the globe. (maybe not noticed) In about 10 percent of cases, it results in a swollen, infected globe. Maybe another pecked her or she got poked by a stick or wire.
Two is systemic. Some chronic immune disease or conditions can lead to infection of the globe from the inside, out.
The third is surgery complications, which do not apply.
These conditions can result in increased pressure in the eye which causes stress on the optic nerve which in reality is glaucoma, not like it matters, you can't do ocular surgery on a chicken.
From what I understand, endophthalmitis can be painful because it involves other ailments such as iritis and keratitis which can be quite uncomfortable, er ah, painful. It is possible your chicken is now in pain or without pain. If she is eating and drinking I figure it is worth trying a couple things.
Google punctured sclera and also endophthalmitis for details on treatment. I think antibiotics are the only chance you got. I hope the other eye is really not affected.
Good luck and take care!