As my best friend would say (jokingly), "Just smack her around until she stops asking stupid questions!"
What I have to wonder, is why she even questioning you training? Seriously, I want to know. I study family sociology (particularly dating and marriage), and I think I have an idea at what she's trying to do (*whipcrack*).
Just tell her, it's good for your health, good for your peace of mind, and it makes you happy. If that's not good enough for her, then maybe she does need to be smacked around.
"Face it. People are fukked. Why would you want a career helping anyone? Go find a mountain and farm sheep for a living." - Serpent on Personal Training
"Its a cool show, but I think this young super man is a very stupid mother ****er." - yenhoi on Smallville
"They could have had the tagline "Watch Joe Millionaire. More stuff will happen," and they'd have been there." - eulerfan on TV watching Americans
"Anyway, I used to pick girls up all the time in the gym when I was in college. We'd hang out until the aerobics classes ended, and then swoop in while all their endorphins were still pumping.
It's like shooting fish in a barrel." - ghthomason on dating
"I would say that there is a greater chance of a paper dog catching and asbestos cat in hell, while in the lost city of Atlantis, Elvis and Ghengis Khan are using butterfly nets to catch the opera-singing monkeys flying out of my butt, but that implies there's still a chance." - Starboy on optimism