What plan does Zeena have when she returns? How does Ethan react at first? What do you think is Zeena's true motive for dismissing Mattie?

When Zeena returns, she tells Ethan that she is going to have a hired girl to take care of everything. Ethan is incredulous and tries to explain that they cannot afford a hired girl, and that they certainly cannot have two girls. Zeena then drops the bomb that Mattie will need to leave..... we can infer that jealousy is part of the reason.