Comparison is the thief of joy, and beware of poison envy.
There is a big difference between accepting yourself and not taking care of yourself. Every body is different, and even if you're happy at a certain weight, you may need to take steps (like exercise) to maintain. Besides, don't you feel better with exercise? I do. I really think the trick is making it "play" and not forcing yourself to do something that you hate. Try everything in the book until you find what you like. And eat what you want, but consider the nutrients you're getting and how you'll feel your best by what you eat. The Mark's daily apple blog is a good site for info on "play" and it's benefits.
I also wouldn't assume that "X" doesn't have to work for her body. She may have habits or disciplines that you don't see. Weight and how we treat our bodies is a very personal thing.
Bottom line. You can be a trendy fatty (if that's what you want to call yourself), but make sure you FEEL GOOD doing it. I feel fabulous at the weight I am now, and I'm still very heavy. But that's because I move and I eat well. It needs to be about health, and if you're gaining constantly, you won't be feeling very good.