Vacation

Clark Griswold (Chevy Chase), wanting to spend more time with his wife Ellen (Beverly D'Angelo) and children Rusty (Anthony Michael Hall) and Audrey (Dana Barron), decides to lead the family on a cross-country expedition from the Chicago area to the Los Angeles amusement park Walley World, billed as "America's Favorite Family Fun Park." Ellen wants to fly, but Clark insists on driving, so he can bond with his family. He has ordered a new car in preparation for the trip, but the dealer (Eugene Levy) claims that it will not be ready for six weeks. Clark is forced to accept a Wagon Queen Family Truckster, an ugly, out-sized station wagon, as the car he brought to trade in (a 1970 Oldsmobile Vista Cruiser [1]) has already been hauled away and crushed.
During the family's travels, they run into numerous mishaps, such as being tagged by vandals in a rundown area of St. Louis, while Clark is tantalized numerous times by a beautiful young woman (Christie Brinkley) driving a flashy red Ferrari. They stop in Kansas to visit Ellen's cousin Catherine (Miriam Flynn) and her husband Eddie (Randy Quaid), who foist cranky Aunt Edna (Imogene Coca) and her mean dog Dinky on the Griswolds, asking them to drop her off at her son Norman's home in Phoenix. After stopping at a decrepit and dirty campground in Colorado for the night, Clark forgets to untie Dinky's leash from the bumper before driving off the next morning, killing the dog. A state trooper pulls the Griswolds off the road and angrily lectures Clark over animal cruelty but accepts Clark's apology; Edna learns of her dog's death and becomes more irate with Clark. Exiting Colorado, the Griswolds lose their credit cards, forcing Clark to have to cash a check for future spendings.
While Ellen and Clark argue during a drive between Utah and Arizona, they crash and become stranded in the desert. After setting off alone in the desert to look for help (becoming a little delirious in the process), Clark eventually reunites with his family, who have been rescued and taken to a local mechanic (who is also the corrupt county sheriff). The mechanic extorts the remainder of Clark's cash only to make the car barely operational. Frustrated, they stop at the Grand Canyon; when Clark cannot convince a hotel clerk (James Staley) to cash a personal check, he takes cash from the cash register behind the clerk's back and leaves the check. Leaving the Canyon, they find that Aunt Edna has died in her sleep. They tie the deceased to the roof of the car, wrapped in a tarpaulin. When they reach Norman's home, they discover he is out of town and leave Edna's body at the back door. Clark eventually meets the Ferrari-driving blonde beauty at a hotel and goes skinny-dipping with her in its pool, but they are discovered by the family before anything untoward can transpire. Ellen forgives Clark, and the couple goes skinny-dipping as well.
Despite the family's misfortunes and the begging of Ellen and the kids, Clark becomes obsessed with reaching Walley World. They finally arrive the next day, only to find that the park is closed for the next two weeks for repairs. Finally slipping into madness and realizing that all his efforts have been for nothing, Clark buys a realistic-looking BB gun pistol and demands that park security guard Russ Lasky (John Candy) take them through Walley World; Ellen and the kids follow, attempting to placate Clark. Eventually, an LAPD SWAT team arrives, along with park owner Roy Walley (Eddie Bracken). Roy understands Clark's impassioned longing to achieve the perfect vacation, bringing back memories of his own childhood years ago. He decides not to file criminal charges against the Griswolds and lets the family - and the SWAT team - enjoy the park as his guests.
The ending credits show various pictures of the Griswolds' vacation as well as the decision to fly home.

Question: Who died in her sleep?
Answer: Aunt Edna