how is cassie "uncle tomming"(miz)lillian jean? why do you think shes doing this?

TJ and Lillian Jean provide interesting foils for one another in this chapter. Just as TJ boasts of his new friends, Lillian Jean does not suspect that Cassie's friendship is an act and continues to be surprised even after Cassie beats her up. Cassie care to not leave any marks on Lillian Jean's face is both pragmatic (there is no evidence against her) and metaphorical, because it shows that Cassie understands the importance of appearances in a way that Lillian Jean and TJ do not.

While Cassie is acting as Lillian Jean's "slave," TJ calls her an "Uncle Tom." In part, of course, this is an allusion to Harriet Beecher Stowe's abolitionist novel, Uncle Tom's Cabin. The word has also been transformed into a derogatory term for a black person who behaves in a sycophantic manner toward whites. This statement is in part ironic because it is TJ who is playing the Uncle Tom figure by ratting out Mrs. Logan to the Wallaces.