I am guessing from the dark scabs within the swollen eye tissue that other chickens have been pecking at her eye. To confirm watch the chickens interaction with her, assuming she is still in the flock and not isolated.
The swelling may not be so much from infection than it is inflammation from being pecked. First, she should be isolated in a safe pen in your run so she doesn't actually leave the flock and lose her standing. Then double down with saline rinses to keep the eye flushed of bacteria, and smooth on the antibiotic ointment twice a day. Eye injuries and infections are very painful. A 81 grain chewable aspirin table twice a day can go a long way toward controlling her pain.
The swelling may not be so much from infection than it is inflammation from being pecked. First, she should be isolated in a safe pen in your run so she doesn't actually leave the flock and lose her standing. Then double down with saline rinses to keep the eye flushed of bacteria, and smooth on the antibiotic ointment twice a day. Eye injuries and infections are very painful. A 81 grain chewable aspirin table twice a day can go a long way toward controlling her pain.