I would suggest that you go to HER vet.
My vet would know all 3 of mine and so would the staff. Have her bring pictures as proof as well. I would bet that there is no vet and there are no pictures that resemble YOUR dog.
Come on`I walk out the door and come back 2 minutes later and mine act like they haven't seen in months. So if this dog didn't recognize her at all he doesn't belong to her.