What reason can you infer for why Alexandra doesn’t think Calpurnia should work for Atticus anymore?

Aunt Alexandra is critical of how Atticus and Calpurnia raise Scout and Jem. She thinks that Atticus gives Calpurnia too much power. Calpurnia is very much a mother-figure to the children. Aunt Alexandra does not think a black housekeeper should have that role in the lives of white children.