The two biggest causes of drooling in dogs is:1. Some sort of dental problem. This could be from an abscess or even a fractured tooth. You're not always able to see these issues as they can sometimes have these problems under the gum line or in the jaw. Since this has come on so suddenly, and since Gracie is still a very young dog, it's unlikely that this is a dental issue.
2. Nausea. Just like humans, dogs sometimes get upset stomachs and that nausea causes them to drool excessively. This is often an acute (comes on quickly) issue that resolves on it's own within a day. The fact she hasn't been doing any vomiting or having diarrhea and is still eating/drinking and acting normally makes me doubt this is the issue, but in the absence of any other causes, it's the most likely reason.
Because she's acting mostly normal, I think it's okay to observe her for tonight and then re-evaluate her in the morning and see if the drooling has stopped. If it hasn't, then you absolutely need to have her seen by a vet, just to be on the safe side.
And of course, it goes without saying that if she starts acting sicker or shows any other unusual symptoms, then you should have her seen right away by an emergency vet rather than waiting until morning.
I hope he's feeling better soon!!