The now-rebellious Tina starts to become upset with her parents, and when they leave her to babysit Gene and Louise while they see Cake (a show presenting patty-cake in the style of Stomp), she invites Tammy, Zeke and Jimmy Jr. to her house and Tammy convinces them to get drunk on margarita mix, until Jimmy Jr. accidentally breaks one of her porcelain toys and Tina tells them to leave.
Tammy, however, steals Tina's notebook full of potentially embarrassing "erotic friend fiction" and blackmails her with it, while Gene and Louise force her to do their chores so they don't reveal the margarita party to their parents.
Gene and Louise, having found out about Tammy's blackmailing, steal back the notebook, but Tina still decides to read her story Buttloose (like Footloose but with "touching butts") only to have the entire cafeteria laugh at her, until Tammy has a sudden bout of flatulence, and the school laugh at her instead, causing her to flee with embarrassment, farting the whole way.
Tina’s such a passive character by definition that her actions usually come as a reaction to her more dynamic family members, and her flashes of independence (such as alter ego Dina in “Food Truckin’”) are muted enough to be overshadowed by the characters dragging her on that journey.
And in terms of figures driving the action, Tammy’s relatively tame, her corrupting influence limited to a series of portmanteaus (Prudabaga, Glamsterdam, snorgasm) that confuse Bob and Linda when Tina uses them.