You might want to check out REI, if you have one near you. They sell road bikes starting at about $520. Depending on how your wife is built, you may want to look into some of the women-specific-design bikes... generally speaking they're made for longer-legs, shorter-torso.
Then again, it's a 12 mile ride. Maybe she could borrow a bike from somebody til she decides if she really likes it or not...?