I'm with toymasters
smokinj, if you want to keep it to just flirtation and sneak tickles with Jennifer, of course that's cool. I wish I worked with a cute girl who let me get away with tickling her now and then.
But if you think you want more, I agree with toymasters - just ask her on a date. Either she'll say "no" and things will remain as they are, or she'll say "yes," and you may get to tickle and play with more than Jennifer's feet.
Jennifer's boyfriend? At the risk of oversimplifying, I'd say he can't be that important to her if she flirts with other guys.