Well first off the botled lemon is a waste since all bottled juices have to be pasteurized by law which kills all the live enzymes. On top of that if she's talking about those little plactic lemon sqeeze bottle I bet that not only in it heavily precessed it also has chemical preservation and who know what. So that would make the Master-Cleanse very unproductive and possibly a total waste just on the juice alone. Add to that that she'll be eating and smoking and drinking coffee that definetly makes it a total waste of time.
The lemonade itself is no magic elixir. It's how/what you do with it that makes it useful. The Master-Cleanse works by giving the digestive system a rest so that the body will use that extra energy to cleanse and heal.
The good news is that she realises she does need to do "something". She sounds pretty set in her ways so it'll be a tough sell to get her to try any of the "alternative" methods. She will hafta make the choice herself and the best you can do is get her some books and or print out some usefull articles or posts if she doesn't have access to the internet.
I tell ya one of the best ways to sell the Master-Cleanse is when folks see the results you get. At least 4 of my friends 2 of which I never thought would try something like the MC in a million years have done it just from seeing how it changed me. Soooooooo..........;+D