Olivia Montgomery is Cooper's younger sister who appeared in the episode I Can't Make You Love Hannah if You Don't. She sends Jackson mixed signals by being very flirtatious with him but then telling Cooper she doesn't like Jackson.
She lies to Cooper that boys were all over her. He believed her until they saw her kissing the pizza guy then Cooper believed Jackson and was very furious with Olivia because it was her who was really all over guys.
Olivia is portrayed by Rae'Ven Larrymore Kelly.