It was the same thing with Hillary Swank. She got really buff for "Million Dollar Baby" but shed it afterwards. She said its just too tough to maintain that physique. Plus, an actress has got to play parts that a muscular build just wouldn't work for.
That's the problem in a nutshell. Personally, if I were rich enough, I'd pay her to stay buff and create roles for her in that condition, in return for regular photos.
