For type 2 (insulin resitance), winstrol may make her glycemic/blood sugar/insulin sensitivity worse. Not good, but dose, duration, diet and training/exercise will prolly make a big difference.
For type 1, I dunno.
If she's a type 2 diabetic, then I suspect that good diet, regular intense exercise, and stuff like ALA and DHA/EPA/Faxseed oil will make a bigger difference than taking AAS. Is she overweight????