Welcome to the forum, what's your puppy's name?
Have you been going to the vet or checking her weight regularly? If she is healthy in other regards and the vet is happy with her body condition, I would try not to worry about her being a picky eater. If you have not had her for a vet check recently, I would call and ask if you could bring her in for a weight check. Any good vet will let you come do that pretty much any time. My vet has always emphasized to me that dogs are like people in the respect that they are better off being a little too lean than a little too heavy.
Following the directions on the package of dog food will have you over feeding her. The best way is to pay attention to her body condition and bump her amount of food up or down depending on how much exercise she's getting and how she is looking. She will go through little growth spurts where she is hungrier and then have phases where she isn't growing as fast. Just pay attention.
She really should be finishing her kibble at every meal and when she doesn't it's a sign that she may not be feeling well (then you think about how much she's drinking, how are her potty habits, firm stool etc. and is she still playing and acting energetic.) or it's a sign she is being over fed. Something else to consider is how much training are you doing with her? Is she getting a lot of training treats? That is something else to take into consideration.
Here is some reading for you:
From a respected site on health:
"Most importantly, I recommend you feed your puppy the amount of food required to keep him lean, which is about a 2 out of 5 or a 4 out of 9 body condition score." Here is the link to the article: Do You Know What to Feed Your Large or Giant Breed Puppy? Feeding Large Breed Puppies - IVC Journal
Here is information on how important it is that she grow slowly: Slow Grow
Here is an article that hopefully will help you not worry as much about her being lean as long as the vet says she's healthy: Add Years To Your Dog's Life | Prevention