I would think that if she is more 100lbs overweight then losing weight will do much more for her than simply worrying about margarine. Probably the biggest problem I see really fat people doing is they end up buying stuff that says "heart healthy whole grains" or "reduced fat" on the box and then they pig out because it's okay. If someone can start eating tasty real food, even if some of it isn't as real as ideal, that's a good start. The good progress itself might lead someone toward a more open mind toward real fats and red meat eventually.
Female, 5'3", 48, Starting weight: 163lbs. Current weight: 135.
Starting bench press: 30lbs. Current bench press: 75lbs.