No Snacks, no sweets, no seconds. Except on Days that start with S. Too simple for you? Simple is why it works. Look here for questions, introductions, support, success stories.
Diets like that are not sustainable over time, so wait a few months and watch her regain the weight she lost. Meanwhile, you will probably have lost a few more pounds. Be ready to tell her about No-S.
"Self-denial's a great sweetener of pleasure."
(Patrick McGoohan's "The Prisoner")