Alexandra treats Calpurnia strictly as a black servant beneath Alexandra's station in life. When she comes to stay with Atticus and the children, Alexandra is sitting on the front porch when Calpurnia and the children come home to find her there. Alexandra's first words are "Put my bag in the front bedroom, Calpurnia." It was an order, not a request, and it was not preceeded by any recognition of Calpurnia as a person worth greeting. Without comment, Cal picks up the heavy bag and starts to take it inside before Jem takes it himself.
After living with Atticus for a while, Alexandra makes her feelings about Calpurnia quite clear. She disapproves of the children having gone to Calpurnia's church, and when Scout asks Atticus if she can go visit Calpurnia at her home, Alexandra intervenes before Atticus can even answer: "You may not."
This incident leads to an argument between Alexandra and Atticus. She insists that it is time for Calpurnia to leave, that she isn't needed anymore. Alexandra also suggests that Calpurnia isn't the proper person to influence Scout as she grows into a young lady. Atticus makes it clear that Calpurnia is one of their family and has done an excellent job in raising the children. Atticus ends the discussion just before Scout returns to the room: "And another thing, the children love her." Alexandra does not argue further, but Scout notices that her aunt is furious.