I have PCOS, am on the pill (Brenda aka Diane) and experience terrible acne when I come off the active tablets. However my dr said this is normal. There are other medications she can use inaddtion to the pill (my dr has suggesed some if I want to go onto them) if the acne really bothers her in that week off.

Before was diagosed (diagnosed April 07), I had severe acne and painful cramping around the time of my period. But no excess hair growth, and not overweight. I had watched my ovulation signs (I just followed my cervical mucous, it can be very accurate and extremely easy to do once you know how), and I realised I wasnt ovulating. I had regular 5 day periods and consistent 34 day cycles, which never varied at all. But I wasn't ovulating during most cycles. I told my dr all these things.

It wasnt hard to be diagnosed - blood test and internal scan. I was diagnosed after I had a blood test that showed that my hormones were way off, and an internal scan that showed cysts on my left ovary.

I don't have diabetes/insulin resistence, so the low-GI diet wouldn't really help the symptoms. But if your SIL does have these issues, and a low-GI diet was recommended for her by her dr, then I would suggest she try it and see how it goes.