Just like any animal the potential for growth is the greatest starting out. The metabolism is running full speed but that growth requires more fuel so they are eating machines once they start. Two rat fuzzies in the same feeding may be a little bit much yet as it would be about 17% if both are 6 grms. However a couple more feedings and you will probably be fine. Do two more feedings at 4 day intervals and reweigh her. Then if the numbers work, give her two and go back to 5 day intervals.