Why was Marguerite sent to work at Mrs. Cullinan's house in I KNow Why the Caged Bird Sings?

Marguerite was sent to work at Mrs. Cullinan's because

"Negro girls in small Southern towns, whether poverty-stricken or just munching along on a few of life's necessities, were given as extensive and irrelevant preparations for adulthood as rich white girls shown in magazines...learning the mid-Victorian values with very little money to indulge them."

In other words, it was expected that such girls learn the delicate skills of "refined" culture, such as embroidering, crocheting, and tatting, as well as table setting for formal dining, and cooking whether it was practical or not.

At the age of ten, Marguerite was sent to the home of Mrs. Viola Cullinan to complete this part of her education. Mrs. Cullinan was "white, fat, old, and without children." She was from Virginia, and had reputedly "married beneath her;" she lived in a three-bedroom house which was run with an exactness which was "inhuman." Mrs. Cullinan was a foolish woman, whose bigotry towards Negroes was clearly evident. She showed her complete disregard for Marguerite's humanity by renaming her "Mary" for her own convenience, having decided that the young girl's real name was "too long." Marguerite responded to her "mentor's" callousness and disregard by purposefully breaking her favorite dishes, thus ending her tenure at the lady's house (Chapter 16).