Cassie was introduced in the episode "Making the Team" where she was shown to be the head cheerleader at Vanderbilt High School. When Laura tries out for the cheerleading squad, she clashes with Cassie when Laura wanted to change some of the cheers.
During the basketball game, Cassie Lynn refuses to cheer for the basketball team because she finds basketball boring, but Laura is able to energize the crowd with the cheers that she made up.
In the episode "Woman of the People," Laura and Cassie Lynn run against each other in the campaign for student body president. Cassie Lynn attempts to blackmail Laura with incriminating photos of Laura appearing to kiss Steve (when acutally, Steve caught her and was using his weight as a brace).
Steve fights back when he has Eddie take pictures of him kissing Cassie Lynn to show her that blackmailing Laura is wrong. In the end, Laura ends up winning the election.
After that, Cassie Lynn is not seen for the rest of the series.