So using other objects for reference...she is twice the size of an Xbox360. Looks fine. These dogs all grow at different rates and at different times. Some have growth spurts early, others have them later on. The slower they grow, the better. Also depends on her genetics...she is a female so she should max out around 70 lbs...I prefer them when they're smaller than 60. Do you know the size of the dam? That will give you some clue as to how big she'll get.
Weight is the most important thing right now. Not too skinny, and make sure she's getting enough food/calories that she has the ability to grow. From the picture, she looks perfectly healthy.