Doubt Regarding Pcos Diagnosis For Relative

My paternal cousin who is 17 years old is all set to start undergrad college in couple of months...she has been having extremely oily skin with acne that becomes worse a week before her periods ...
Her cycles are ok, like once in 28-30 days but she complains of heavy bleeding sometimes..
No abnormal hair growth..either or face or body..hair is normal..
Mild hair loss in scalp..
Also has put on considerable weight, I.e 6 kg in just couple of months,.
Of course heredity plays a role..her mother and grandmother have oily skin and have had pimples too..even during middle age..weight gain and hair loss Maybe due to stress of studies and exam pressure too..
She consulted family doc who prescribed topical ointment and based on symptoms she told to do pelvic ultra sound and suggested a consult with gynaecologist to rule out PCOS as so many teenagers are having this problem...
She will be going to the gynaecologist in another one month after finishing exams..
Few doubts she has:
What is the likelihood of developing PCOS if there is no family history and at what age usually women get it?
Is it necessary that ladies who have PCOD should have irregular period?
Is a pelvic ultrasound enough to identify presence of cyst or Any other tests required too?
Any other blood test?
If the pelvic ultra sound is clear and shows no cysts, then she doesn't have PCOS?
Ladies kindly clarify doubts..

 

Can anyone advice regarding my query? So many views but no replies.

 

Thanks for your reply...will convey to my cousin.
One doubt..
If the pelvic ultrasound does not show any abnormalities that means she does not have PCOS right?