The vet can manually palpate the third eyelid and see how easily it proplapses. They can tell you if the problem was incidental or if it is getting worse and requires additional operations. If it is incidental and the eyelid appears normal, your vet will probably tell you to monitor her and if the third eyelid doesn't prolapse again, then you probably having nothing to worry about. If the problem recurs, by all means I'd have her see the doc, preferably an opthamalogist.