If you think she will be 40/50 pounds or more as an adult, I would feed a large breed puppy food to be on the safe side.
And no, I doubt that she is fully grown at 8 months. That can happen with small breeds but not larger ones.
Nutrition in Large Breed Puppies
Another thought, if you are not 100% sure of her birthdate she could very well be a little older….
Sometimes a vet can tell by examining their teeth.
Shelters often minimize age to make the pup more desirable for adoption. Sometimes only by a few months, or they may be going by the little information that they have.
