In Walk Two Moons, what happened to Sal's mother? What are some clues that help readers infer the ending?

It is not until Chapter 42 that the reader discovers the reason that Sal’s mother is not coming back is because she was killed in an accident. She was travelling by bus to Idaho to see her cousin when the bus swerved off the road at a sharp turn. The bus went over the edge, and the only survivor was Margaret Cadaver, who had been sitting beside Sal's mother and had become friends with her as they traveled together. Sal's mother told Margaret all about Sal and her husband. This is how Sal's father knew Margaret and talked so much with her. While Sal tried to convince herself that there was a romance brewing between Margaret and her father,in reality it was only her father clinging to the last person who had talked to his wife before her death. Margaret wanted to talk to Sal about her mother, but this was too "real" for Sal, who had not yet accepted the fact that her mother was not coming home.

There are some hints and clues, but at no time until this chapter does the reader clearly know the outcome. This is related to the fact that Sal cannot completely believe her mother is dead. The clues are clear with a second reading. Otherwise, they just seem to be random observations of Sal's. For example, in Chapter 2, Sal says that she is afraid of cars and buses, since that is how her mother was killed. In Chapter 3 she says that she is afraid of pregnant women. Sal's mother had suffered a miscarriage, which led her to want to visit her cousin in Idaho, as she was someone who knew her when she was a little girl, before she was a wife and mother. When Sal says that she needs to get to where her mother is in Idaho by her birthday so she can bring her back home, her father and grandparents tell her that she is fishing in the air because they know she is dead. When Ben asks about her mother and if she is coming back, Sal is momentarily confused. At heart, she knows her mother is gone, but she has not told anyone else about her mother's death.

When Sal’s mother left of her own free will, Sal did not understand. When Sal learns that her mother is not coming back, her father tries to tell her that she intended to come back. She did not plan to desert her family permanently, although it turned out she did. This is why Sal decides to help Phoebe find her mother, as she is convinced that if they can find Mrs. Winterbottom, it will somehow help her to deal with her own mother’s death.