Sarah was a girl who appeared in the Season 3 episode, Moving On. In the episode, she has a interest in Justin,
though Justin doesn't share the feelings back because he still has feelings for Juliet. At the end of the episode, she goes on a date with Justin. It is assumed they are no longer together since Sarah doesn't appear in anymore episodes and its most likely due to Justin being right about it being federally illegal for her to write her phone number on a dollar bill as it is marking U.S. currency.