How and why does Shelia change in An Inspector Calls

J.B Priestley's An Inspector Calls, is a political statements towards the bourgeoise and how they are unacountable for their actions in society. Shelia Birling is the youngest child of Mr Birling. Shelia represents what Priestley hopes is a move towards social change through taking responsibility. We see Shelia developing as a character, firstly, through stage directions and then in her behaviour towards other characters; mainly her father.  To begin, Shelia is ditsy. This can be seen through her "hastily" kissing Gerald, and her childish behaviour of still calling her parents "mummy" and "daddy". Her behaviour then begins to change as we see her take responsibilty for her role in Eva's death. She is the only character to do so initially, by stating that "it was my own fault", when her family attempted to defend her actions. Furthermore, we see a shift in her behaviour from a childish grown up to a modern woman, by her illustrating her strength in walking away from her cheating fiance. At the beginning of Act 1, we see Shelia excited at the engagement ring that Gerlad "wanted [her] to have", to her unemotional tone of "Gerald kept her-" the shift in language that Shelia expresses, highlights how her character has developed.  J.B Priestley, arguably, uses Shelia as his own socialist mouthpiece. It was common knowledge that Priestley was a socialist, and as the novel was written in 1945, it wouldn't have been a popular opinion to have. Therefore, Priestley uses Shelia as a mouthpiece which allows for the audience to distinguish between right and wrong. As Shelia comes to the decision that she is to blame for Eva's death, we as a audience member view this behaviour as enlightened. It is the contrast between Shelia's behaviour and Mr Birling that highlights why Priestley presents Shelia as enlightened. Mr Birling represents the upper class, elites, that Priestley is actively against. Therefore, it can be seen how Priestley uses Shelia to demostrate his own agenda for the progression of society