After the New Directions' performance at regionals, Sue calls Quinn into her office a second time and says how impressed she is with Quinn and that's why she has decided to let her rejoin the Cheerios. Quinn gladly accepts the Cheerio's uniform and promises not to let Sue down.

Does Quinn go back to the Cheerios?

At the beginning of the new school year, Quinn is reinstated as head cheerleader. ... When Sue forces Quinn, Santana and Brittany to choose between cheerleading and the glee club, all three initially go with the Cheerios to retain their popularity, but are later convinced by Finn to defect to New Directions.

Does Quinn join the Cheerios in Season 3?

In The Purple Piano Project, Santana and Brittany both rejoin the Cheerios, but Quinn refuses, saying she wasn't interested and instead joins The Skanks. During an interview with Jacob, Santana says that her senior year is all about getting on top of the Cheerios.