Guess you weren't aware that "You" is just a "stage name" version of her name that she recently started using (i.e. "recently" meaning just within the last year or two). Originally, most websites/fansites have been romanizing it as "Yuu".
Subsequently, we've already got a thread for her under the "original" spelling of her name "Kikkawa Yuu" in the H!P girls thread.
http://forum.jphip.com/index.php?topic=16154.0