What breed is she? It’s unusual for a dog to have not had their first heat by 15 months unless they are a very large breed (Dane, Newfie, St Bernard, etc) is it possible that she had a heat cycle and was diligent about keeping the blood licked up? Could she have had a silent heat with no bleeding at all? Is she acting like herself? I’d be concerned if she’s more lethargic than usual, drinking more, or refusing food. Does the discharge smell at all? Sour, foul, etc? Based off the pictures I’m really concerned that this is pus and there is potentially a uterine infection known as pyometra. When pus is being discharged from the vagina the cervix is still open and allowing the pus to pass through, but once the cervix closes it is known as “closed pyometra” and is fatal when left untreated. I’m a veterinary technician and if shown these photos by any of my clients I would 100% ask them to come in for a same-day appointment or would be putting together an ER referral.