She obviosly means well, the mother probably had parents just like her and it's all she knows. With the information age upon us it still amazes me how people don't go searching for good info on really important things, like raising kids. Heck before I got my last dog I did probably 15 hours of reading internet articles about different dog things, from diet, excercise, to obedience and training.
Because of it I have a well mannered, fun, playful loving healthy dog and it's because I didn't assume I know everything and went to the net where experts give their info away freely. Sure there is some bullcrap stuff on the net, but once you research a few different things, for example research planting a garden. Anyways, once you research a few things, you get a good feeling for what is crap and what is honest people sharing thier experiences.
Allthough at the end of the day what the mother has to realize is that she can give the daughter the information, but since the daughter is a free willed living organism, it's ultimately up to her if she wants to adopt that knowledge into a working lifestyle. Everyday, people choose to be fat. Sure some people just don't know, but most of them know or know they should know, and also know people who could help them, or where to look to help themselves.
Most block that out, grab another serving of donughts and coffe, and then have a monthly breakdown where they promise themselves they are going to change and lose the weight. Well making a decision to lose weight once a month does not trump making a decision to be fat 180 times a month, or approxomately every time they eat. Throw in another 12 if you count making the decision to not work out a minimum of 3x a week.
Perhaps if the mother understood that you can't force someone to do something, and allowed it to be the daughters choice, while giving her the tools and encouragement to succeed, perhaps the daughter would make the choice.