If the tear staining has just started, I'd ask what it the dog's environment has recently changed. If she switched him to a different food, that could be the cause.
Otherwise, allergies of some kind could be flaring up. As mentioned, hair could be irritating the eyes, causing excessive tearing, or the tear ducts could be blocked.
Otherwise, allergies of some kind could be flaring up. As mentioned, hair could be irritating the eyes, causing excessive tearing, or the tear ducts could be blocked.