Apple cider may slow the emptying of your stomach so that you feel full for longer and it also reduces the glycemic impact of a carb meal (for the same reason). Other than that it doesn't do much, and if you're like me it won't curb appetite nearly enough by itself to cause weight loss. She will still need to count calories and intentionally eat below maintenance. The reduced glycemic impact may be more relevant to folks that are already insulin resistant/obese. It is not obvious to me that it helps non-obese non-insulin resistant dieters. On the positive side, it seems to be a reasonably harmless supplement to try (cost aside).