When Winnie takes Mae Tuck's place in the jail cell so Mae can escape before she hangs, Winnie becomes an "accomplice" to a crime. That makes her a criminal, but because she is underage, she can't be punished as an adult would be. The constable feels "she badly needed punishing," but he can only release her to her parents' custody. Winnie's family grills her about why she helped a murderer escape.
Of course, she can't explain that she saved the universe by helping an immortal woman escape an ineffective hanging and by assuring that the source of the magic water would remain secret. So she tells the part of the story she can tell—that she loved Mae. After that, her family supports her emotionally, although they still confine her to her home and yard "indefinitely." She actually becomes famous and a bit of an icon to the other children in town. One day, Winnie rescues a toad from a dog and decides to protect it by pouring the bottle of water Jesse gave her onto it. She reasons that she can always get more if she decides, when she turns seventeen, to drink the water and marry Jesse.
Readers wonder whether she did get more water and drink it. The epilogue clarifies that she did not. When the Tucks return to Treegap in 1950, they find Winnie's gravestone and learn that she died two years ago. She married and had at least one child. She never drank the water.
At the end of Natalie Babbitt's book Tuck Everlasting, Winnie has been dead for two years, having died an old woman at the age of 78. Her age at her death matters greatly to the plot of the book.
When Winnie was eleven she met a family with the last name of Tuck. For a lot of reasons she does not understand at the time the Tucks are very secretive and unsociable. At one point they essentially kidnap Winnie after she discovers their secret--water from the spring near their house has made them immortal, freezing them at the age when they first drank it. Winnie becomes close to the Tucks, especially the son, Jesse. She helps them overcome someone who wants to possess the water, and to escape from the area (and a murder charge for Mae Tuck), so their secret is not discovered. Before they leave, Jesse gives her a vial of the spring's water, and tells her to drink it when she is seventeen, and to find him. The story skips then to a return to the area by the Tucks, almost seventy years later. They haven't aged. In the cemetery they find Winnie's tombstone; she has been a wife and mother, something the Tucks made clear to her could not be successfully done by those who were immortal.