Went through the same thing 2 years ago - when my son was 13.  I couldn’t believe it - had he been on steroids all his life for nothing?  He was originally diagnosed with a very high 17OHP and we had ’marker’ DNA testing, which supposedly confirmed the diagnosis - full genetic testing not available in those days. The fact that he had zero levels of 17OHP since that first reading, was suddenly considered ’not normal’ for CAH 13 years later.  He went through a short synacthen test, and then a long synacthen test (4 days of injections and off medication), which still showed zero levels of 17OHP, indicating CAH was not the correct diagnosis, although cortisol was also zero.  Adrenal Hypoplasia was therefore considered but further DNA testing confirmed CAH after all.  The adrenals had become completely dormant - hence the zero levels of 17OHP.  Overtreatment in the early years was the possible cause and I am pleased to say that the adrenals have now been ’kick started’ and we have normal 17OHP levels for a CAH child.  Good luck - I know how frustrated and upset you must feel, but there must have been a good reason for your daughter to have been diagnosed in the first place and if there is any doubt, it should be checked out.  DNA testing is the best solution, but if there is still doubt, then full gene mapping is a must!