Why is Hedda so mean in particular to Aunt Juile?

Why is Hedda so mean.... in my opinion i guess her character is meant to expose the problems with upper middle class society through her own bad ways. She has married into the lower class and she wants to prove that she is still the same person she was before she was married. She wants to prove that she is still better than George and aunt Julia. Furthermore, it also might be because Mrs Tesman is still trying to control George life when in turn Hedda wants to control it. What do you think?