Overboard

Spoiled heiress Joanna Stayton (Goldie Hawn) is accustomed to the life of the idle rich with her husband, Grant Stayton III (Edward Herrmann). While waiting for their yacht to be repaired in the rural hamlet of Elk Cove, Oregon, she passes the time by hiring local carpenter Dean Proffitt (Kurt Russell) to remodel her closet. He puts up with her rude and condescending attitude and produces some quality work which is dismissed by her because he used oak instead of cedar, despite her not having specifically asked for this at the start. When he agrees to redo the closet after he gets the money for the work done she refuses to pay and they have an argument, during which he astutely notes that she is inventing things to complain about because her life is so pampered and boring (this gets overheard by the yacht's crew on the intercom who applaud him for telling her off), which concludes with her pushing him off the ship and dumping his tools in after him.
Later that night, as the yacht sails away from the harbor, Joanna goes out on deck to retrieve a lost piece of jewelry and falls overboard. The next day the local TV news shows a story about her having been picked out of the water around midnight by a garbage scow. She is suffering from amnesia and is taken to the local hospital where no one can figure out who she is. Once Grant realizes she has fallen overboard, he sails back to port to get her. After seeing her mental state and her lashing out at hospital employees, he denies knowing her and returns to the yacht to embark on a spree of parties with younger women.
After seeing her story on the local news, Dean, a widower living in squalor with four sons, decides to seek revenge, or more specifically, get Joanna to work off her unpaid bill and losing his tools. He goes to the hospital and tells her that she is Annie, his wife of thirteen years and the mother of his sons. The hospital staff is eager for her to be gone, but they need binding proof he is responsible for her, and he bears no legal documentation to do so. He is granted her release by telling them about a small birthmark on her behind, which he saw on the yacht when she was wearing a revealing swimsuit. She reluctantly goes home with him. Once there, she is appalled by his residence, but feels some obligation to pitch in, having come to think of herself as "Annie".
At first, Joanna has difficulty dealing with Dean's sons and the heavy load of chores. She soon adapts, however, and learns to cook, clean, do laundry, and care for the family dogs. As she masters her responsibilities, she learns about the boys' school and family issues and that Dean is secretly working two jobs to make ends meet. She begins to fall in love with him and his sons, and starts streamlining the money problems with more efficient budgeting. She also tells off a persnickety teacher who gives the boys a hard time, accusing the school of being more concerned with ranking than the well-being of their students.
Seeing Dean struggle, Joanna makes his dream come true by helping him design a miniature golf course based on her untapped knowledge of the Seven Wonders of the World. Although he has also fallen in love with her, he does not tell her the truth about her real identity for fear that she will leave. Even when he attempts to confess when she discovers a pair of expensive monogrammed underwear (which are actually hers) leading to think he is cheating, his friend, Billy (Michael G. Hagerty), takes the blame. He, who also doctored photos of them to cement the alibi of their prior relationship, tells Dean in private he covered for him because his family needs Joanna.
Meanwhile, after Joanna's mother, Edith (Katherine Helmond), threatens Grant (who has been lying that Joanna is "too indisposed" to talk to her), he reluctantly ends the partying and returns to Elk Cove to retrieve her, tracing her to the Profitt residence. She greets him and her memory is instantaneously restored. She is shocked and hurt when she realizes that Dean lied and has been using her for months. She returns with Grant to the yacht where Edith and Dr. Korman (Henry Alan Miller), their bumbling psychiatrist, are waiting.
Joanna now finds her old lifestyle stuffy and pretentious. That evening, after doing shots of tequila with the crew, she turns to Andrew (Roddy McDowall), her loyal butler, and apologizes for her poor treatment of him. Surprised and pleased, he observes that unlike most people, she has been given an opportunity to see life from a different station than that to which she was born. He also tells her that she is the one who can decide how to use the new perspective. Realizing how happy she was with Dean and his sons, she commandeers the yacht and turns back toward Elk Cove. When Grant finds out, he admits he never loved her, and commandeers it.
Meanwhile, Dean and his sons attempt to get Joanna back with the help of Billy's friend who is in the Coast Guard. When they catch up to the yacht, she and Dean both jump overboard. An incensed Grant attempts to shoot her with a bow and arrow only to be unceremoniously booted overboard by Andrew, who promptly gives his notice of resignation. Safely aboard the smaller vessel, Dean is impressed that she left Grant for him, but she says the money and yacht are actually hers. He then asks her, "What could I possibly give you that you don't already have?" She looks at the boys, smiles, and replies, "A little girl."

Question: Who has been lying and using Edith for months?
Answer: Dean