Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Purdy has a watery eye, is squinting, and is bothered enough not to want her dinner.
If her eye is tearing heavily that can cause a moist dermatitis (like diaper rash) which can lead to red, weepy skin and fur loss.
If her eye size looks normal, not drawn back into her head or swollen and very large looking compared to compared to her other eye, and her lids aren't droopy, and because only one eye is affected I would be suspicious of some sort of trauma (possibly from another pet, wild animal or plant material?) or a foreign body (grass awn, grass blades) in her affected eye.
I am glad to hear that she herself isn't rubbing her eye but squinting does usually indicate discomfort/pain.
Perhaps being a curious cat she stuck her nose somewhere into plants and scratched her eye or got some plant material in it.
If she is feeling fine otherwise there are a couple things that you can try at home. You can purchase all of the things I mention below over the counter at the local drug store.
You can start with flushing that eye copiously with sterile saline, that should soothe her eye and hopefully remove any sort of foreign body.
Then apply artificial tears every few hours or the next few days to keep her eye cushioned and hydrated.
Apply a small amount of Polysporin ointment 3 to 4 times daily to her eye for 4 to 5 days to prevent an infection.
I do recommend trying to keep her in a low light setting, at least for the next 24 to 48 hours.
If this is a mild scratch then it should start significant healing over the next 48 hours and her third eyelid should regress.
If she isn't much better in a couple days, or her eye becomes swollen or really red or she is pawing at it, she should be looked at by her veterinarian to try and diagnose her particular problem.
Best of luck with your girl, please let me know if you have any further questions.