swollen eye?

hello, my family rescued three hens a couple of days ago. this is the first time we have taken care of chickens and so we have a very slim amount of knowledge but we are trying our hardest to provide a good life for them.

I'm posting here because one of the hens has had an incredibly swollen eye the entire time we have had her. the picture is included, I hope it is somewhat easy to see - her eye stays shut like this the vast majority of the time. I'm not sure if this should be chalked up to an injury before we got her or if it is a health concern. If anyone could offer their advice or give any suggestions, it would be extremely appreciated.

I'm also happy to provide more pics/info if needed. thank you!