Phentermine seems like a counterproductive drug for someone in our lifestyle.
If it is for your girl, I would DEFINITELY suggest that she make even just minor adjustments to diet and exercise, before suggesting she use this drug.
I'd sell it to her this way - even just modest changes that yield an average weight loss of 1 to 2 pounds per week, will produce a net weight loss of approximately 50 to 100 pounds this same date in 2017. FIFTY TO ONE HUNDRED POUNDS! Assuming she is looking to lose much less than this, changes to diet and exercise look like a better alternative than weight loss drugs with potential bad side effects.
Plus, she can maintain (or even gain) muscle doing it this way, versus the certain muscle loss (firmness) that will happen if she loses 30 lbs in 45 days using only drugs.
Yes, I do realize the hypocrisy of an AAS user taking this stand, but I think if you'll consider my logic above, and consider the differences in losing weight versus the goals we as weightlifters have, it make sense.
A girl wanting "to lose weight" thinks that she wants to "lose weight" when in reality, what she really wants is for her body to look differently. These are two different things! Phentermine use versus diet/exercise changes will both achieve the goal of "losing weight", but diet/exercise modification will produce much more desirable effects on body composition change (wanting her body to look different), which is what she really wants anyways.