"Mirah, my sister, leave us!" said Ezra, in a tone of authority.
She looked at her brother falteringly, beseechingly—in awe of his decision, yet unable to go without making a plea for this father who was like something that had grown in her flesh with pain, but that she could never have cut away without worse pain. She went close to her brother, and putting her hand in his, said, in a low voice, but not so low as to be unheard by Lapidoth, "Remember, Ezra—you said my mother would not have shut him out." (66.16-17)
Mirah's feelings towards her father are complex. On one hand, she fears him and wants to run away from him. On the other hand, she feels obligated to look out for his interests because he's still her father, after all. Mordecai (Ezra here, since that's what Mirah calls him) doesn't feel the same obligation toward their father. As a result, Mirah pleads with him to remember their mother and to think about what she would have done in this situation.