the healthiest way of losing weight is eating better and exercising more- burn more calories than you take in and the pounds will come off. it doesn't make sense to add whatever is in these diet pills to your body.
if she's looking for an alternative, ask her to try a cleanse instead. ReCleanse is good because it focuses on changing your eating habits while you take the colon/liver cleansing pills, and it allows you to eat small meals thruout the day and not force you to starve - several of my friends have done this and they feel better after it too because it flushes you out and hopefully starts you on the pattern towards eating more natural and fewer processed foods. they have lost weight as a side-effect of the cleanse.
recleanse
here is a very detailed article on Alli that your sis should read before she starts taking it-
Alli weight-loss pill: Does it work? - MayoClinic.com
and here's another good article on whether weight loss pills work or not-
Over-the-counter weight-loss pills: Do they work? - MayoClinic.com
"Dietary supplements and weight-loss aids aren't subject to the same rigorous standards as are prescription drugs or medications sold over-the-counter. Thus, they can be marketed with limited proof of effectiveness or safety. Vendors can make health claims about products based on their own review and interpretation of studies without the authorization of the FDA. However, the FDA can pull a product off the market if it's proved dangerous. For the consumer, it's hard to know what you're getting, or even if the list of ingredients matches what's in the bottle. Many weight-loss pills contain a cocktail of ingredients — some with more than 20 herbs, botanicals, vitamins, minerals or other add-ons, such as caffeine or laxatives. How these ingredients interact individually and collectively with your body is largely unknown. And using them can be a risky venture, especially if you're taking other medications.
Your own scrutiny and curiosity are your best protection. Read labels closely and talk with your doctor or pharmacist about any dietary supplements you're taking or considering taking."