When my son was 4 years old the plan was to move him out from every 3 months to every 4 months.  The ped endo said that it was because his levels were excellent and everything was tracking excellently.  Unfortunately, it was at that time that the liquid cortef went bad and all hell broke loose. 

He just turned 8 the other day and he is still on every 3 months due to the growth hormone protocol.

It sounds like your daughter is doing just fine.

Good luck.