Well I used to think I was fat in the eighty grade. And I got people to buy me stackers. Diet pills are not good for people that age. Its not legal either you are suppose to be 18.
When I took stackers, I felt like my heart was going to explode it speeds up your heart rate and can cause a heart attack. I wouldn't suggest it. You also do not have an appetite. And if she starts taking them then she will be very "wired" and not want to eat.
Look up some information on diet pills on yahoo or google I am sure you can find some answers. But I would suggest it. If anything let her go to the doctor and if they think she needs to lose a few pounds they will give her something healthy and that won't harm her body or put her on a diet.