lurkette is sneaky.
Your name suggests at least a passing interest in martial arts.
Tell her you're really interested in starting some sort of class, but again that you don't know if you could do it alone, and that you'd want to have a sparring partner, etc. Not only would you both become more fit, not only would you both learn a defensive art, but it'd also teach a little more self-control and maybe she'd stop drinking so much beer (or, as I affectionately refer to it, "a yeasty meal in a bottle".)
Good luck.