There are all sorts of reasons for weight gain, and "settling down" is a major risk factor for some of us. Your lifestyle simply changes - when you eat, what you eat, what time you get for excercise (or other personal pursuits) changes. Maybe men are better at not allowing co-habitation change these habits than women are, but women, as a rule, adapt to the man. I gained a bit of weight when I first got married because I was cooking for him and eating the way he ate.
People are way to glib about the idea that all you have to do is excersise more and eat less. People have different set points, and this woman's is kind of high, evidentally. Read "Rethinking Thin" for the science on the subject - doctors and scientists have known the same thing for ages: what you're meant to be, you're meant to be. You can fight it for awhile, but unless you want to fight every minute of your life, you're going to be what you're going to be. And fighting is exhausting. It doesn't leave time for the rest of life.
However, this young woman shouldn't be so glib about a large weight gain in a short period. She shouldn't be so unconcerned - she'd be better off finding out what's going on and losing it - if practicable - while she's young and energetic and before she begins to suffer health related problems from it. Also, I think people do have a responsibility to their mates to make an effort - you try to keep yourself well-groomed and attractive. You brush your teeth. You bathe. But partners also have to understand that physical changes do happen, and weight isn't entirely in one's own control. That's got nothing to do with Oprah, that's the way of the world. People used to understand and accept that, but now media has convinced us all that we're supposed to be the same.
