I agree - there's an issue of Avengers where we see her sneaking off to the pantry to eat some ice cream when she's feeling a bit blue after an inter-team squabble. I see her as someone who makes an effort to keep in reasonable shape, but since there isn't really a physical aspect to her powers, there's no particular reason for her to spend hours in the gym or anything. Her role in the team is to stand back and go 'hocus-pocus - death ray, turn at a right angle and blacken the neighbor's azaleas!' - she doesn't hit anybody or anything.