She would be wasting her time as she won't be doing the "MC". Do you have a copy of the book? Give her that to read. Does she have access to the Internet, send her some site links with information on the diet and other links you think are important. The Master-Cleanse may very well help her actually quit smoking.
And, above all, tell her you love her and would like her to stick around for many more years to come. Meaning, she needs to gain control of her health. I say this from personal experience. There's nothing more devastating that seeing a parent battle cancer after years of smoking and neglecting their health. It's never to early nor too late to try and get her on the right path for her health.
She may need to take baby steps first, like adjust her diet to a pre-cleanse diet, but at least she's starting to take interest in doing something. And you can thank yourself for making her more aware! It's your commitment to the Master-Cleanse that's getting her interested.