3 times? I panic at 1.5x... ouch.

If you brought it up, she might say she'd work on it, but that's no guarantee of change. Getting down to slimness from 3x just seems.. unrealistic. At any rate, if she doesn't change enough for your desires, then I don't think this'll be a happy relationship for both parties. Unless you're somehow equally unattractive and you're not telling us, it's probably for the best you found one of those girls you think of when you dream of what could be.