Do you know how old she is?
I can't tell as the photo gets kind of blurry enlarged, but does that look like it could be puss? Chicken puss looks a bit like a hard chunk of cheese, not that thin yellow stuff humans and other animals get. It might smell too.
Does she have any symptoms like runny nose, runny eye, or is her eye swollen, etc.?
She could have gotten pecked in the eye and it became infected.
I would rinse it out with a saline solution, then see if you can tell what it is.
If you believe it's an infection/puss: Terramycin is for eye infections. But before that, I would try get that out. Apply hot compresses, then with a tweezers, gently pull it out. It won't come out too easily. You may need to keep applying hot compresses then try again.
This video is gross but shows it being done. Be sure to put Terramycin in when done.
If you don't think it's an infection, there could be other causes too but we'll wait for you to come back so we know some answers.