My son was diagnosed with CAH (he turned out to be a carrier).  Meanwhile my daughter had such similar symptoms that I was sure she had it too - hairiness, early puberty, irregular periods.  But it turned out that she isn’t even a carrier but has PCO.  So to try and answer your question, if your cousin was diagnosed with PCO she could really have CAH or at least be a carrier.  The only way to know is with a blood test.  Her doctor should test her because maybe infertility caused by CAH would be treated differently than PCO.  Also, her husband should be tested if she’s a CAH carrier.