When a girl has insulin resistance, what are the effects?

Not good.... Insulin resistance causes diabetes and predisposes to atherosclerosis. Over time as the body demands more and more Insulin there is burn out of the islet cells in the pancreas making diabetes worse and requiring Insulin for treatment. Regular exercise, weight loss to achieve ideal body weight and healthy diet are ways to overcome Insulin resistance and it's ill effects.
See below. Insulin resistance occurs in patients who have abdominal obesity. It often results in the development of diabetes because circulating Insulin is less effective. It is also present in the metabolic syndrome which is also characterized by increased triglycerides, increased blood pressure and decreased hdl. Such patients are at increased risk for cardiovascular disease. Ir improves with weight loss.