Rabbits under 6 months of age are still growing and therefore need higher protein and more nutrients than an adult rabbit. This is usually accomplished by feeding more pellets than you would an adult rabbit. Often it is recommended to free feed pellets to young rabbits, but this can present problems if the bunny prefers to eat pellets over hay, and isn't consuming enough hay and getting enough fiber in their diet. I've found the best way to ensure a young rabbit is getting enough pellets but not more than needed, is to make sure they are also eating a pile of hay each day, that is about the same size as their body. If they aren't, reduce pellets some. If they are eating more hay than this, increase pellets. The times you wouldn't apply this is if pellets seem to cause health problems for an individual rabbit, such as mushy poop or stasis issues. Then you have to find the right diet for your particular rabbit.
She may be eating more because she is going through a growth spurt. 1/2 cup may not be too much for a growing baby, depending on her size and breed. But even if she is consuming more pellets because of a growth spurt, you don't want to suddenly increase pellet amounts by too much. Pellets should always be gradually increased to allow a rabbits digestive flora to adapt and limit possible digestive problems. Better to feed more grass hay to make up for the increased appetite, while you gradually increase the pellet amount over several days, while still ensuring in the end that the 'body size' pile of hay is still being eaten.
