Yes it is. If one tear duct is prone to clogging - due to narrowing or a congenital malformation - allergies could exacerbate the problem, causing the tear duct to narrow still more and causing tearing, while not causing a problem in the other, healthy, eye. This is exactly the case with Sparky and, in fact, is the case with myself. I have one eye and sinus that are affected by allergies while my other eye and sinus are not (unless the pollen is very heavy). My sinus on the left was crushed by my dear Bella and although I had surgery to open it up, it is still less able to withstand seasonal allergies. The OP may of course want to get a second opinion, but since she's had a vet out repeatedly and the discharge is clear and does not get worse, it doesn't sound like a serious issue.