How does Rosa escape her tutoring session with Geoff Honeyman in the novel, My Sister Rosa?

Rosa finds her father’s phone and sends Geoff messages that she pretends are from David. Because no one has warned Geoff about Rosa’s personality, he does not suspect anything is wrong when he gets a message telling him to leave before Rosa’s parents get home. After he leaves, Rosa takes advantage of the freedom to run away and go to the park where she plays chess.