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 that helps the team win. After this, Cassie Lynn is kicked off the cheering squad and this made her hate Laura more.
In Food, Lies and Videotape, Miss. Steuben admonishes Cassie Lynn for her lack of effort in her cooking class. She tells Cassie Lynn off that if she wants to pass her class, she's going to have to learn to cook like everybody else by working with her hands. Miss. Steuben proves it by taking off the latex gloves and putting raw dough in her hands.
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 actually, Steve caught her and was using his weight as a brace) to make her drop out of the race.
Steve fights back when he has Eddie take pictures of him kissing Cassie Lynn to show her that blackmailing Laura is wrong. When she pointed out that he kissed her, Urkel tells Cassie Lynn off that he knows how rumors work after catching her threatening Laura. So he's returning the favor to her by letting Eddie take the pictures to the school newspaper and the students will believe that Cassie Lynn willingly kissed Urkel, which will ruin her reputation unless she listens to what he has to say. He is able to convince her they can do this fairly by letting the students vote and decide for themselves. In the end, Laura ends up winning the election. Starting in season 4, Myra becomes Laura's main nemesis and Cassie Lynn is never seen or mentioned again for the rest of the series, implying she moved away.