hercufles: You like the sofa that much? :D
StingingVelvet: If a relationship doesn't have honesty then its just fuck buddies with obligations. That doesn't mean you say "bitch you so fat", it means you say "honey for both our sakes I think we need to be more healthy. I think you're beautiful now, and I always will, but lets be the best we can be" or something. It depends on the situation.
Being obese is not good for anyone. This idea we have to tip-toe around it like its a race or sexual orientation is just making people fatter.
This is true, but you are making the assumption that it is an honest question to which she expects an honest answer, and that is almost never the case.
She doesn't actually want to know whether she's fat, or whether you think she's fat. She's insecure about something (you get to guess what; it may not have anything to do with real or imagined flab) and wants strokes.
While ravishing her on the spot is excessive in most situations, it's the general direction in which your answer should tend.