That's a new one. :?
I have no idea what it might be- but I would try applying Blu-kote to it since that will treat bacterial and fungal infections. Spraying a cotton swab and dabbing it on would probably be the best way to apply it without getting it in her eye itself.
It doesn't look ulcerated like you would see with a herpes type lesion, but I would check her nether regions just to be sure she doesn't have some type of venereal disease that transferred to her eyelid.