This is only me pumping out ideas here, but your charrie could be gay and 110% obsessed with how my character's boobs are bigger than hers. This is how you know I watch too many tsundere anime, haha! (By the way, was it an unnwritten requirement that we had to use an anime avatar?)  

Additionally, your charrie could also be a druggie or a gambling addict.  Oooh she could be a lesbian behaviorist who's always analyzing everybody's behavior, but dropping subtle hints to Sara.  Why the hell do I keep making her gay?  Making myself a mental note to never have biscotti and Cpt Morgan after midnight. :/