Her adrenals will be appropriately suppressed when her blood work levels come in a range that your pediatric endo is comfortable with.  Those tests could include 17OHP, androsteinedione, DHEAS, testosterone, renin, electrolytes, and maybe others.  When these levels are in the acceptable range, the adrenals are suppressed and then the amount of medication given hopefully matches as closely as possible to what the adrenals would naturally make if they worked properly.  This is replacement dosage.  Sometimes it takes a bit to find the right dose for your child.  Our pediatric endo runs bloodwork one month after a medication change is made.  But my kids are older now, and I honestly don’t remember how often we ran it when they were as young as your child.  I do remember that from about age 2 to 9, dosage levels were pretty consistent.  Then it gets a little erratic again at puberty. I hope that helps a little.