Spanglish

The film starts with Cristina Moreno applying to Princeton University. She tells the story of her childhood in her college essay.
Flor Moreno (Paz Vega) is a poor, Mexican single mother who is hired as the housekeeper for John (Adam Sandler) and Deborah Clasky (Téa Leoni), their kids Bernice (Sarah Steele) and Georgie (Ian Hayland), and Deborah's alcoholic mother Evelyn Wright (Cloris Leachman), a rich American family in Los Angeles. John is head chef at a popular restaurant, Deborah is a former businesswoman turned stay-at-home mother, and Evelyn is a former jazz singer.
Flor speaks very little English. She does not mention that she has a daughter, Cristina (Shelbie Bruce). John, Evelyn, Georgie and Bernice are very likeable; Deborah, however, is uptight, her behavior often upsetting both households.
Summer comes and Flor is needed 24/7 at the Claskys' summer home. Unable to communicate well in English, Deborah finds a neighbor to interpret. Flor reveals that she is unable to maintain these hours because she has a daughter, so Cristina is invited to come stay with them.
Cristina interprets for her mother. She impresses Deborah, who begins to treat her like a daughter, taking Cristina shopping, getting her hair done, enrolling her in a private school, and showing her more love than she does the sensitive Bernice.
Flor becomes unhappy when it appears that Cristina is influenced by Deborah, in part because she wants Cristina to keep in touch with her Mexican roots and working-class values, and partly because Deborah is overstepping her bounds. Flor objects to Deborah's actions to John, who apologizes.
Flor loses her temper when she finds out that John has given Cristina over $600 in cash for a minor task. She threatens to leave but John convinces her to stay for Cristina's sake.
Flor begins to learn English so she can communicate better. She becomes closer to John, who is having difficulty with Deborah's self-centered behavior. The now-sober Evelyn realizes that her daughter is having an affair and that her marriage is in trouble. She pleads with Deborah to end the affair, telling her she'll never get another man as good as John.
Deborah confesses to John that she cheated on him. John walks out and gives Flor a ride in his car. They go to his restaurant, where he cooks for Flor and they enjoy the "conversation of their lives," feeling love for one another.
Flor quits and takes her daughter home, upsetting Cristina, who got along well with the Claskys. On their way home, she tells Cristina that she can't go to the private school anymore either, upsetting Cristina even more; she screams in the middle of the street that Flor can't do this to her and that her life is ruined. Flor loses patience with Cristina after she asks her mother for space. Flor explains to her daughter that she must answer the most important question of her life, at a very young age: "Is what you want for yourself to become someone very different than me?" Cristina considers this on their bus ride home, and they make up and embrace.
The film ends with Cristina as an adult, years later, acknowledging that her life rests firmly and happily on the simple fact that she is her mother's daughter.

Question: What has Deborah done to put her marriage in jeopardy?
Answer: affair