How and why does Shelia change in An Inspector Calls?

When the audience is first introduced to Shelia, it is clear she is out of control of her life and her marriage. She attempts to warn Gerald in a humorous manner not to become a "purple faced old man" from drinking too much Port, yet the stage directions imply that she has a genuine concern of this as she speaks "possessively." Being part of the younger generation and a woman, Sheila is forced to convey her concerns as lighthearted, and to passively accepts the wills of Gerald, a male who is also her superior in terms of social class. Therefore, at first presentation Sheila accepts the situation she has been given by her parents and her husband, willing to accept submission.However, after meeting Inspector Goole, Sheila takes responsibility of her actions and regains control of her life. For example, when Gerald offers her the ring again, she refuses to wear it straight away stating that she "must think." Sheila progresses in the play as she refuses to be forced into re-marrying Gerald, despite it being the wishes of her family. Sheila realises the similarities between Gerald and Mr Birling through the references to Port, as Birlings first line in the play was "pass the port Edna." Therefore, she understands that she doesn't want the same type of marriage as her parents, and she doesn't want to maintain their values. As a result, Priestley uses Sheila to symbolise the changing attitudes of a younger generation, who a 1930's audience would relate to after experiencing the War and new Labour reforms.