I think you need to find small things that she can do at home that will help her get a bit fitter without losing weight. There are chair dancing videos and such that will help her move a bit and be more comfortable without losing weight or stopping eating.

Depending on where you are, there also may be workout classes for fat people. There are in NY and SF, at least, that I know of.

I hope it's a big success...I may be in SF in July, and I'd love to come to a second meeting!