Josephine's goopy eye

When we rescued Jo a few months ago, she had an infected eye. It gummed her eye shut; it slowly got better until it was just a goop running constantly and building up. The vet said it might be viral and she couldn't do anything about it, but not to worry about other cats catching it because "they were immunized against it." It has never really gone away. When she gets really stressed it gets bad, but generally it's just a clear, mucous-consistancy goo that leaks out of her right eye. The vet says not to worry, but it's not clearing up. Ideas?

How old is Jo?

Is she is a kitten then she may need antibiotics in order for it to get better. It is common in kittens and I've heard that if they have it as kittens sometimes it occurs when they are older.

Jo is about 15 months old. Far from a kitten

Bump for advice.