Sick but doesn’t seem sick?

Ta

We have a dog that will be two August 5. We’ve had her since she was four months and she’s been eating the same food since we got her which is also the food her foster family was giving her. She eats a cup of dry food at about 7 am and 6 pm. We don’t give her any table food. For the past week or so, she’s been throwing up, once or twice a day, what looks like undigested or only partially digested dog food. Usually in the morning before she eats the first time or sometime after eating the second time. Other than that she has been acting perfectly normal, still enjoys playing and walks and being rowdy. We made a vet appointment but they can’t get her in until next week. Has anyone experienced this before? Any ideas what’s causing it or what the vet will say?