What do i do about my fat girlfriend?

Okay, so I have a wonderful girlfriend of two years, and i'm in love with her. since we started dating, she's been steadily putting on weight. Now she weighs over two hundred pounds, a good fifty more than when we started dating. the strange thing is, i've found that i really like the extra weight on her. Her bigger body is amazingly attractive to me. But lately, she's been pretty serious with her workouts, and i'm worried she might start losing weight. I've never told her how i feel about her weight gain, should I? on the other hand, if she's committed to some healthy goals i don't want to discourage her. So should i tell her? or not?