Look at how Quinn’s actions trace back to being heterosexual.
Her heterosexual leads to her getting pregnant, which defines her in season one.
Her heterosexual relationships with Puck and Finn motivates her actions in season one.
She is kicked out the house because her heterosexuality caused her to get pregnant.
Her relationship with girls (e.g. Rachel) are about conflict over Finn and therefore her heterosexuality.
Even when she’s trying to be popular her heterosexuality is continually brought up again with her relationships with Sam, and later her quest to be prom queen with Finn.
Why must all of Quinn’s storylines come back to the fact that she is heterosexual?