Has she had a tilt table test? If so, do you have the results from that? Most of the people here who have NCS and POTS didn't actually "develop" POTS later; for those who were diagnosed with NCS first and then POTS later, it is almost always the case that they just didn't get the correct diagnosis originally but their signs/symptoms have not changed whatsoever (i.e. the POTS could/should have been diagnosed at the same time as the NCS).
I can give you the link to the diagnostic criteria for POTS. Many doctors don't know these, or have mistaken ideas about certain aspects of them; this leads to missed diagnoses and misdiagnoses. If you think that your daughter has POTS, discuss it with her physician and be very specific about discussing the diagnostic criteria so that you can get a clear idea of whether you and the doctor are on the same page about what the diagnostic criteria are. If not, you may need to take a closer look at that; if your doctor has mistaken ideas about what POTS is, then things get tricky. Some patients may choose to present the doctor with printed materials to show the doctor what the real criteria for POTS are; other patients may not want to get into an "ego struggle" with a doctor and may just let it go and head directly for a second opinion.
Here is the information:
http://www.medhelp.org/health_pages/Neurological-Disorders/Dysautonomia--POTS-Diagnostic-Criteria/show/1011?cid=196
If you have more questions about POTS (or anything else of course), just let us know.
Best,
-Heiferly.