Add me to the list of people who say call your vet!
For my part, I used to be less militant about calling the vet for any little eye issue. But then this last spring my mare came in with a super swollen, runny, eye.
I figured I'd give it a day and see.
The next day it was no better, maybe even worse, so the vet came out. Turns out that my mare has a disease called ERU or "Moon Blindness" that had gone undiagnosed for years.
The time I took calling the vet ended up costing her precious vision. Now she's much blind-er than she would have been if I had just called the vet as soon as I noticed swelling.
Not to mention that over the years, prior to this event, she had had swollen eyes before that horsey friends of mine said were "nothing". I believed them but if I hadn't and called a vet instead, she could have gotten treatment for her ERU soooo much sooner. If she had been diagnosed sooner, she would still probably have more vision that she has now (with ERU, each "episode" = vision loss).
ERU is mostly likely not the issue with your girl but that's just an example of why it's so absolutely important to at least talk to a vet when you have a horse with a swollen, tearing, eye.
Fabio - 13 year old Arabian/Lipizzan gelding
Rest peacefully, Lacey.