Kitten with low immunity system?

Hello, I have a 9 and 1/2 month old female cat. She comes from a street cat litter. She's extremely sociable, has good appetite and is very playful. Since the beginning, she's had a dark reddish running from her eyes and usually has very mild dry dark stuff in her nose. Even though she had been to the vet (different ones) a couple of times before, only 3 months ago did another vet find she had gengivitis and conjuntivitis. The first suspicion was FelV but the result was negative. The vet prescribe elugel for the gengivitis and conjunctilone for the eyes. The gengivitis is almost gone and we have started giving her food with l-lysine and especially designed for cats with oral problems. The problem is that the conjuntivitis is persistent. I have treated her twice, it goes away completely to come back again, even though in a mild form. I know it's probably virus, but what else can I do? I've been told by another vet she simply has a low immunity system.