How could the ending of "Where Are You Going, Where Have You Been?" been prevented?

The ending could have been prevented by better parenting. If Connie had received more guidance and support from her parents, she may have felt less inclined to test the limits of her emerging sexuality.
The dysfunction in Connie's family is evident in the way her parents treat her. While her father largely ignores her, Connie's mother is antagonistic and critical. She constantly denigrates Connie for her looks. The impression we get of Connie's mother is that she is unhappy with her own fading looks and jealous of Connie's fresh beauty.
Connie's mother constantly compares Connie to June, her older sister. June is twenty-four and works as a secretary at Connie's high school. She has plain looks, but she is a hard worker. When she is home, June is helpful, conscientious, and dutiful. She is constantly praised by her mother and her aunts for these traits. On the other hand, Connie is persistently belittled by the same group of family members.
Because she has such an unhappy home life, Connie often sneaks across the highway to a sleazy diner to meet boys. One day, she sees a strange man watching her as she walks across the restaurant's parking lot. The man drives a gold-colored convertible jalopy. The only words he says to her are "Gonna get you, baby." These words come back to haunt her later when he turns up at her house while she is alone.
The man tells her that his name is Arnold Friend and that he knows everything about Connie and her family. He also tells her that he knows what her parents and sister are doing and how long they will be away. Arnold maintains that Connie is the only girl for him and that he means to have her. He threatens to hurt her family if she calls the police. The story ends on an ambiguous but ominous note. The implication is that Connie leaves with Arnold, but her fate is undetermined.
It is noteworthy to recognize that Joyce Carol Oates received the inspiration for this story from the case of "The Pied Piper of Tucson," a serial killer who murdered young girls and dumped their bodies in the Arizona desert in the mid 1960s. By all indications, Connie may have escaped Arnold's attention if she had never frequented the diner. From the story, we know that Connie met with boys at the diner as an act of desperate rebellion.
To recap, Connie may have been less inclined to test her limits if she had had more support and love in her life.