First, congratulations that she has stopped smoking, I know how hard that can be. When you detoxify your body one of the side effects of that is losing weight. Your fat cells surround the toxins to protect your vital organs so when you do a whole body cleanse and release those toxins you will drop pounds.
I know there are a lot of cleanses out there, make sure she researches them and finds the best one for her. I myself have found a product that cleanses in 9 days or you can do a 30 day cleanse. This program provides your body with the nutrients that it needs and you don't feel deprived. The first day can be a little hard but I am sure that is the same with every cleanse. If you would like more information you can check out http://www.lysaharvey.isagenix.com
Hope this helps and if you would like more info please feel free to email me.
Good Luck and Congrats again on quitting smoking.