Hey Aurora. Sorry, I am a bit of a lurker but saw your post. I also have PCOS. Until about 2 years ago I was a size 8, weighed less than 8 stone, had a period every month (ish! Sometimes would be 6 week cycle and occasionally a lot longer, but generally pretty regular) but apparently you always have pcos, it's not something that develops. That's according to my GP, although I remain sceptical. My point being, you don't always have the general signs.
However! Having said all that, the NHS mentions the below as diagnostic criteria:
A diagnosis of PCOS can usually be made if other rare causes of the same symptoms have been ruled out and you meet at least two of the following three criteria:
you have irregular periods or infrequent periods – this indicates that your ovaries don't regularly release eggs (ovulate)
blood tests showing you have high levels of "male hormones", such as testosterone (or sometimes just the signs of excess male hormones, even if the blood test is normal)
scans showing you have polycystic ovaries
If you don't have these, I would either push for further testing or if you know already these aren't true for you I would take her 'diagnosis' with a pinch of salt personally :)