See in text (V)
The verb “twit” means to taunt, tease, or ridicule, especially by referencing something embarrassing. In this context, the narrator means that Marjorie was ridiculed by Bernice’s relationship with Warren, Marjorie’s main love interest.
"that her chance at beauty had been sacrificed to the jealous whim of a selfish girl. ..."
See in text (VI)
Notice that Bernice focuses on beauty as the opportunity that she has lost rather than status, connections, or identity. Beauty is singled out as the mechanism through which women obtain social power in this period. Marjorie destroyed Bernice’s chances by causing her to cut her hair.