The answer seems indeed to be the second option: Beneatha is protective of her mother.
Mama, Walter, and Beneatha are characters in the play A Raisin in the Sun. The play's plot revolves around the money that the family - the Youngers - will receive after Mama's husband passed away and how each member of the family has a different point of view on how it should be spent. Walter, Mama's son, wants to invest the money on a liquor store. Beneatha, his sister, would like to use the money to invest on her own education. Mama, however, wants to use the money to buy the family a house, which was her late husband's dream.
Even though Beneatha would like to have the money invested on herself, she does not want the money for herself. Throughout the play, she comes to realize that, if she is depending on such money to achieve her dreams, she is not as independent as she claims to be. Also, her relationship with her mother is a healthy one. Mama is not one to question or to boss Beneatha around. They are happy and understanding. That is another reason that would lead us to believe the stage directions and the line show how Beneatha is protective of her mother. Her behavior toward her brother is in fact a bit judgmental and crude, and that "sharpness" is also a big part of her personality.
