how and why does Sheila Birling change in An Inspector calls?

Priestley describes her as "a pretty girl in her early twenties, very pleased with life and rather excited," She really has nothing in life to be sad about. At the same time Shelia seems rather naive about the world. By the second and third acts, Shelia discovers how she unwittingly played a part in Eva Smith's life and death. Shelia becomes a little more self-aware of her place in society as well as her entitled life.