Why does Aunt Alexandra stay with Jem, Scout and Atticus?

Atticus is very busy with the case of Tom Robinson.

Aunt Alexandra believes they need a feminie influence in the home.

Aunt Alexandra also wants to give Scout some "feminine influence".

Textual evidence:

"Jem's growing up now and you are too," she said to me. "We decided that it would be best for you to have some feminine influence. It won't be many years, Jean Louise, before you become interested in clothes and boys--"