Stepsister from Planet Weird (2000) on Netflix

Plot summary

Megan Larson is fourteen and longs for her divorced parents to get back together. She also hopes Cutter Colburne, a popular boy at her school, will be her boyfriend. Then her mother Kathy meets Cosmo Cola, a nice man who behaves very strangely, and the two become engaged. Cosmo's daughter Ariel is stranger still. She hides under her father's car whenever the wind blows, speaks in a sophisticated manner, wears many layers of clothing to protect her essence, and cannot ride a bicycle. The students at school find her behavior cool and revolutionary, and her teachers call her mannerisms poetic. Ariel dislikes the town and wants to return to Yukon, where her boyfriend Fanul lives. Megan and Ariel both want to break up their parents, so they join forces, but their plans do not work.