Priestly believed in equality and wanted social justice where the rich take responsibility for their actions and for those less well off. He used the Birling family and their victimization of Eva Smith to illustrate his message.
Sheila Birling also played a big role in the death of Eva Smith. She was immature used to getting her own way, "I insisted." Sheila is a stubborn bad tempered character as she shows when she says, "I was in a furious temper." In Milwards shop Eva is asked to model the dress Sheila wanted to buy. Sheila was jealous of Eva because of her looks and the fact the dress suited to Eva better than herself. She imagined that Eva was laughing and was furious at Eva and demanded the manager to sack her, "I told him if he did not get rid of that girl, I'd never go near the place again and I'd persuade mother to close our account with them." Like her father. Sheila uses her power and wealth against Eva. She knows she can use this to get what she wants because rich families like the Birlings can put pressure on shops like Milwards. After the event Sheila thinks about her actions and regrets them but at the time did not care what happened to Eva. "If she'd been some miserable plain creature, I don't suppose I'd have done it." She matures as the play progresses. She is very 'stressed' by her mothers refusal to take responsibility "Now, mother don't you see?" her broken language shows how upset she is by Eva's death and her families guilt.
I think Mrs. Birling more to blame than Sheila