I think its a lovely thought and shows that you really care about your friend. This is an extremely sensitive subject though and I can see why you'd be worried about her getting upset. How about getting a spa gift certificate that can be used towards weight loss or any number of other things that could be pampering. Also, from a weight loss support perspective, I think getting her a personal trainer for a few months may actually cost the same and help her a lot more. If you're super-close to her why not talk to her and let her choose..