Foamy bubbles in the corner of the eye often mean that there's inflammation involving the eye and tear duct. This can happen when there's a foxtail in the eye, but respiratory diseases can also cause this sign (think of sinusitis). Some respiratory diseases in chickens are really contagious and dangerous to the flock. Have there been any new birds added, or any visiting birds or people who keep chickens? If so, contagious disease is really high on the list and you need to consult a vet and watch the rest of the flock very closely.
I would separate this bird from the rest so that you can monitor her and also to try to give her a low-stress environment to help her fight this. Separating her at this point might not stop signs from appearing in other birds, since diseases spread fast, but you can at least help this one by giving her her own space, food, and water. If you have foxtail grass in your area, check the eyes for foxtails; it would be unusual to have them in both eyes, but not impossible.
If other birds start showing signs, the matter could be serious, and I'd visit a vet who sees poultry. Good luck!