"I am having trouble getting a hold of my secondary character's voice. I thought if I tried writing a short story with her as the focus it would give her more life in my mind and future writings. It will also fill in some background info I hope."
This is excellent, especially since you haven't taken any courses and came up with the idea yourself...
It's a great tool (even if you suck at writing shorts, because honestly, if you never intend to publish it, you can do whatever you want IN it, breaking all sorts of "rules" that would keep you in the slush pile, because the whole point is for you to get a better grip on the character)...it call also be used to get you out of writer's block on a novel.