How does Priestley present the character of Sheila in 'An Inspector Calls'?

Sheila Birling is arguably one of the strongest and most complex characters in 'An Inspector Calls', due to her depth of feeling, and the change that her character undergoes throughout the play.
At the start of the play, Sheila is childish and materialistic, representing the failings of typical middle class girls in the early twentieth-century, as Priestley sees them. When Gerald presents her with a ring, she says, 'Oh, Gerald, is it the one you wanted me to have?' This use of the passive case, 'me', suggests that Sheila is subordinate to Gerald, as younger women of the day would be. Her emotion and focus on an item of jewellery, saying 'Now I really feel engaged', suggests that she is more obsessed with the material aspects of her relationship than her feelings for Gerald. Finally, she says, 'Look, mummy, isn't it a beauty?' The use of childish language, 'mummy', highlights her immaturity at this point in the play, while her focus on beauty foreshadows what we learn later: that she ruined Eva's career out of jealousy for her appearance.