How hard do you have to press to feel them (when dekka or Zo are in agility weight you can feel most of their ribs too..but no spine) How is her coat, her energy etc etc? Some dogs are naturally thinner than others (not saying she doesn't need weight..but that maybe you don't need to be stressed about it) Also she will still be growing, so I wouldn't worry too much if she is otherwise in great health.
(interestingly studies have shown that mice, and other animals live much longer, healthier lives when kept quite thin vs what is considered ideal...man I am going to die early
but my dogs will live decently long lives)