Poor chickie! I'm wondering if she got pecked by another chicken. It looks like that is a younger chicken... is she in with older ones that could be picking on her? Is her other eye okay? I would suggest separating her so that her eye has some time to heal without getting pecked at more. Other chickens can make injuries much worse if they don't leave it alone to heal.
As for treatment, if it doesn't continue to swell or become pussy or runny, I would probably just leave it alone and monitor it. Should the swelling increase or her eye begin producing a discharge, I would suggest plain old Neosprin applied in a dollop right to the eye. I have used Neo with great success for eye problems in chickens and other animals. Of course, monitor her and let us know how she is doing. Good luck!
From your other thread, you had a chicken with foul smelling discharge and a swollen eye that looked like coryza. This could be an injury, but more likely, could be the same type of infection starting. Are you treating the other chickens still?