Several different things could be going on here. 1) an injury. Was she pecked? Her eye is swollen and there looks like there is dried blood along the margins of her eyelids. 2) an infection. Which could have resulted from the injury. 3) a sinus infection which could make her eye look like it does.
Is there any discharge or drainage from her sinus? Is she sneezing? The fact that she is acting lethargic could directly stem from the possibility that she has an infection.
I would flush her eye with normal saline like you find in Refresh Eye drops or Optifree. You can put antibiotic salve on your finger and rub it around her eye. Some of it will get into the eye. She probably needs to be on an antibiotic also. Do you have an avian vet nearby that could take a look at her? Might be advisable especially since she is acting lethargic and weak, signs of a systemic infection or that the eye is really bothering her.
Hope she gets to feeling better.