My advice to her would be, Lose those 7 lbs and then again go for the skinfold test and see if her body mass index is still in the healthy range or not. Because in my opinion, by losing 7 lbs, she won't be in the underweight category. Rather she will feel perfect after losing this extra weight. Then she should try to maintain this weight and follow a healthy life style. She must focus on a healthy diet for her weight loss that she can continue later in the life as well.