I'd tell her, but don't expect to get a miracle. I've found that with Weight Watchers and the gym the only one who really matters in all of this is yourself--I don't have a Weight Watchers buddy any more, I found that I relied too much on her to inspire me to go, and when she didn't, I got mad at her (and myself too for not going for me). Since I've gone the solo route, now the only person to blame if I don't go or don't do well is the one who is really responsible.

Might be better off in the long run to enjoy the people who attend the classes all the time and make new friends there!