I think you are talking about the moment when Scout criticized Walter Cunningham for putting too much syrup on his food.
Calpurnia wanted to point out that it was inappropriate to criticize company and that we should respect all people's ways. Fortunately for Scout, Cal chose to do this privately. This is why she called Scout into the kitchen. She tried to scold Scout for this behavior privately. This may have been done to respect Scout or to protect Walter's feelings. Maybe it was done for both reasons. Whatever the reason, it all shows that Calpurnia is sensitive to all people's feelings.
In Chapter 3 of To Kill a Mockingbird, while Walter Cunningham eats "dinner" with the Finches at the invitation of Jem and Scout watches with disapproval, Scout narrates that Calpurnia "requested my presence in the kitchen."
When Jem first invites Walter Cunningham to come home with Scout and him, Walter looks eager, then his face darkens, probably for the same reason that he declined the quarter that Miss Caroline offered him earlier for a lunch ticket. But after Jem asks him, "Don't you like butterbeans?" the enticement of this food cannot be resisted, and Walter comes home with the Finch children.
As Atticus engages Walter easily in conversation, Scout watches Walter pile food onto his plate. While the polite Atticus speaks of farming issues, Walter interrupts to request molasses syrup. Calpurnia is summoned and she brings a pitcher to Walter, who proceeds to pour this syrup over both his vegetables and his meat. As he does so, Scout is appalled.
He would probably have poured it into his milk glass had I not asked what the sam hill he was doing.
Scout embarrasses Walter, who quickly sets the pitcher down, puts his hands in his lap, and lowers his head. Perceiving the boy's embarrassment, Atticus shakes his head at Scout, who cannot keep quiet:
"But he's gone and drowned his dinner in syrup.... He's poured it all over...."
At this point, Calpurnia escorts Scout into the kitchen where she furiously scolds Scout. She explains to Scout that some people do not eat in the same manner as the Finches, but it is impolite to criticize them. "That boy's yo' comp'ny and if he wants to eat up the tablecloth, you let him, you hear?"
Scout protests that Walter is not company; he is "just a Cunningham." Calpurnia reignites and scolds Scout some more, telling her that her family may be better off than the Cunninghams, but it does not matter because Scout's behavior is disgraceful. She then tells Scout that since she cannot act "fit to eat at the table" in the other room, she better sit and eat at the kitchen table.
Having finished her scolding, Calpurnia sends Scout back to the dining room with "a stinging smack." Scout retrieves her plate and completes her meal in the kitchen, thankful that she can be hidden from the others in her shame. Scout tries to retaliate against Calpurnia by promising to drown herself at Barker's Eddy one day when Calpurnia is not watching her. She also blames Calpurnia for getting her into trouble with her teacher since she taught her how to write.
This little scenario with Calpurnia presents a view of Calpurnia as not just the stereotypical "colored maid" of the era, but a woman who is empowered by her employer to act as a surrogate mother. As Scout complains to her as she would a mother while in the same manner, Calpurnia reprimands Scout, "Hush your fussin'."