She is most likely insulin resistant. Or she might have hyperinsulimia, which is the release of too much insulin--that would account for her low fasting insulin levels.

The best supplements to deal with either of the above conditions are GTF chromium, gymnema sylvestre, vitamin D, calcium, and magnesium, as well as a good quality multivitamin (2 per dose). These supplements are also good for PCOS.

PCOS has been linked to vitamin D deficiency and can be comprised of multiple conditions:
Genetic predisposition.
Insulin resistance or hyperinsulinism (high blood levels of insulin).
Obesity.
Hyperandrogenism (excessive production of male hormones).
Abnormality of the hypothalamic-pituitary-gonadal axis (organ/hormonal disorder).
Environmental chemical pollution (hormonal disruptors)
Food adulterantion (excitatory amino acids, for example)
Chronic inflammation