Aunt Alexandra comes to stay with Atticus and the Finch children because of the Tom Robinson trial for the most part. Atticus will be very busy during the trial and won't have time to take care of the kids even with Calpurnia's help. Another reason she is there is because she feels she must do what she can to protect the children. She knows that the trial may get ugly and she disagrees with Atticus's involvement anyway, so she thinks that she can shield the children from any ugliness that may occur. She feels that she must be there, too, to protect the family name. Aunt Alexandra believes that Atticus is raising the children incorrectly. She sees him as being much too liberal with the children and she wants to counteract that. She is a staunch conservative in all her views. She feels that one's family background is more important than what one does and that is not how Atticus has raised Scout and Jem. Ultimately, she loses this battle of child-rearing philosophies. Her reasons for being there are varied and each reason reflects what kind of person she is.
SHE IS CRAZY
she is like mount everest:cold and there
I agree with luannw and afroman4073, but what is she like?
i think that what luannw said was completely correct but i think another reason was so that she could be with scout more and try to make her chang into a girl and to stop acting like a boy but luannw is correct