It looks like it might be an abcess, but I think it looks more like a tumor
Is it actually her eyelid or is it right above her eye?
If it feels like it has alot of fluid inside it (abcess), take a
sharp box knife and cut it open so it can drain. After that you should probably bandage her eye shut, so that it can heal and not get infected.
If you don't think it's an abcess, then I would take her to a vet if you have one avaliable. If you really don't want to spend alot of money on her, then you could just put her down yourselves as soon as you notice signs of it hurting her or making her (noticeablly) sick. Chickens are incredibly tough, so she might not be showing signs that she is in pain
right now, but I'll bet that hurts her. If she starts acting sluggish, I would send her to heaven asap.
Keep a close eye on the rest of your girls and (if she is still running loose) keep an eye on her to make sure that she isn't getting picked on. If the other girls start pecking her, it could lead to an eye injury, and if her eye get's infected it has a straight path to her brain, so be
extremely careful to not let that get infected.
Hope this helps
and that it isn't anything serious!