How does Sheila's character change reflect some of Priestley's ideas?

At the start of the play, Sheila is presented as the model daughter. She speaks to her parents formally,what defers to what they say.... she's quiet, submissive. By the end of the play, Sheila comes out of her shell and is willing to challenge her parents views, to tell them what she thinks, and to do so independently, unafraid of their reactions. She changes because the Inspector's words, as well as his presence, open her eyes and give her the courage to speak out.