Adipex?
http://www.drugs.com/pdr/adipex_p_tablets.html
Am surprised that it is being prescribed IF your friend already had WLS. How far out is she? If over 2 years, has she not lost a significant amount of weight? It may be that they are using it to jumpstart her weight loss and get her back on track. IF she is less than 2 years out, then I am surprised.
More information about her situation would be helpful.
The 10 to 15 lb bounce back weight is pretty common/normal. Going back on "diet pills" doesn't seem like a good idea to me. I'm really surprised.
With the weight gain my questions would be:
1. Are you eating a low carb diet?
2. Are you exercising 4 to 5 times a week?
3. Are you eating enough protein?
4. Are you getting in a minimum of 64 oz of fluids (non-caffeine) a day?
5. Are you following the rules?
6. Are you grazing?
If the answer is No, then there is things that could be done with behavior modification that would achieve the same goals. Just my opinion ... I'm not a doctor.
I hope she does OK and that her doctor keeps her monitored during the process.