I took Kymmi to the vet today. The vet did a thorough examination of her eye and didn't see anything wrong with it. She said that maybe she'd gotten something in it or had scratched it causing it to swell and the third eyelid pop out like that. She said her eye wasn't irritated at all today. She thinks it was just a minor injury that has resolved itself. I hope so. It has looked totally normal for 2 days now.
Thanks for the replies and advice.