What are Atticus's reasons for why Calpurnia needs to continue to work for the Finch family?

He knows that he will be away from home a lot with the case.

"Alexandra, Calpurnia's not leaving this house until she wants to. You may think otherwise, but I couldn't have got along without her all these years. She's a faithful member of this family and you'll simply have to accept things the way they are. Besides,

sister, I don't want you working your head off for us-you've no reason to do that. We still need Cal as much as we ever did."

"But Atticus--'

"Besides, I don't think the children've suffered one bit from her having brought them up. If anything, she's been harder on them in some ways than a mother would have been . . . she's never let them get away with any- thing, she's never indulged them the way most colored nurses do. She tried to bring them up according to her lights, and Cal's lights are pretty good-and another thing, the children love her."

Sorry I thought the question read Alexandra.