Why did Deena slap her mother?  Answer the above question based on the context below:  Deena Marten is a 15-year-old who has become a rebel since dating Garret Lexau, another rebellious teen who was suspended from school for hitting a teacher. Deena no longer keeps any of her promises, skips school and leaves the family home whenever she pleases. Her newfound harsh attitude upsets her mother, Cynthia, who once enjoyed a close relationship with her daughter. Cynthia is frustrated because the lines of communication have broken down between mother and daughter. Cynthia's relationship with her own mother is not entirely pleasant. Although Cynthia's alcoholic mother advises her daughter to be stricter with Deena, Cynthia does not  heed the advice. For example, she tidies Deena's bedroom, a chore which Cynthia has consistently and politely reminded her daughter to do. When Deena discovers what Cynthia has done, she is less than grateful and reacts violently and ends up pushing her mother. Adam, Deena's younger brother notices the impact that Deena's behavior has upon his mother and drinks alcohol in order to forget about the family problems. At one point, Cynthia and Deena's relationship seems to improve, until Cynthia finds out that she has been skipping school. Her confrontation leads to an argument, during which Deena slaps her. Although she admits to Garret that she liked hitting her, Deena later apologizes to her mother, only to ask her to cover for her absence at school.
The answer to this question is:
Cynthia finds out that she has been skipping school