[anonymously]

She is only 9 months old, still a pup. She will continue to fill out till she is 2 years old.
She does not look thin to me, she looks fit.
Frankly, if the vet says she is healthy, I would just continue what you are doing.
Also, some dogs are naturally thin, just like some humans.
She is actually better off health wise being on the slim side, imo. Obesity can cause a multitude of problems.