why did mama say " if thats the case daisy, i don't think i need that little food"?

Mary Logan and Miss Crocker are discussing the book situation. Mary has covered the offensive labels with brown paper and says that maybe someone should come and see all the things they need in order to conduct a proper school. Miss Crocker accuses Mary of being ungrateful for what they are given, but Mary doesn’t really see the need to be grateful for being handed someone else’s trash.

Miss Crocker says something about not "biting the hand that feeds us," meaning that the blacks should be grateful for the books they get from the whites and should not suggest (by covering the labels) that they don't appreciate them. Mary doesn't think too much of the "food" (books).