It might be useful to have her join a children's group that specifically focuses on nutritional and weight issues. In addition, I would definitely recommend that she start to participate in some sort of physical activity. Even if she is not athletically inclined, there are many different non-traditional sports that will allow her to get the benefits of exercise.
In general, type II diabetes has its onset during adulthood, so she is not significantly at risk for it until the later teenage and early young adult years. I would recommend that you monitor her for possible symptoms of diabetes as she starts to go through puberty.