Hello and thank you for using this site to help you.
Getting groomed can bring on stress , so that might be a cause, or the dog could have caught a virus from one of the other dogs in the grooming facility.
However if you actually saw something in the stool it does sound like it could be something she got into and it is just coincidence that it came after the grooming.
I would bring in a sample of stool to be tested by your vet for parasites or protazoa as this too can cause vomiting and diarrhea. This can also cause the stool to have like a casing to it.
But if the dog eats any non food items such as raw hides , toys, clothes, etc. then there may be a blockage of the intestinal tract as this will also show vomiting, diarrhea, lack of appetite and lethargy. This would need surgery.
For today , in case it is a self limited virus, I would fast her for 24 hours then start a bland diet of boiled chicken and cooked white rice. If she still has a problem after this , it is advised that you have her examined especially given her age as puppies can downturn quickly.
Make sure she has water during the fast.