I haven't heard of this before. It could be an incomplete shedding in which case it would be harmless, it could be some kind of eye infection, or it could be the beginnings of a cataract. I am not an expert.

Maybe you should try putting her in quarantine so you can keep an eye on how she's moving, whether she's eating enough and so on. If she's slower, not climbing, or not hungry an infection of some sort seems most likely.