>>1
Help her lose weight. Don't make her lose weight for the sake of losing weight. Show her how to have a richer and healthier life.
Pick up some intense sport with her, cook her a few exquisite and superhealthy meals, and once she's hooked teach her how to make them herself. Also don't forget that it's unhealthy to lose weight too quickly. Plus, it'll make her skin sag, if her skin isn't given enough time to adapt: stretchmarks in reverse.

Remember: fat can be lost, but a horrible personality goes to the core. Fat can be lost within a year, but a headcase will take decades to cure. And a (figuratively speaking) lame person will take years to develop into something good. Years of learning, evolving and adapting. Good people don't grow on trees.

If her weight bothers you because of your family, rather than due to concern for her health... Something's seriously wrong with how you feel about her.