chick with an eye problem

[lacontenta]

My littlest chick isn't growing like the rest of them. (12 days old) I see her eat, drink & poop. She isn't picked on by the rest of them & even gets right in the feeder & gets her share. However, when she's not eating or drinking, she's kind of lethargic...maybe she's just conserving her energy. Her one eye is shut most of the time. 3 times a day when I feed, water & play with them, I open it. I noticed a bit of tiny foam around her eyeball. What is this?? How can I help her. I'm worrried I may lose little Lucy