Why did Elizabeth kill the children?

On Beulah Height was written by Reginald Hill. The book describes the past of the Yorkshire village of Dendale, which was flooded by developers to create a reservoir. This was carried out shortly after the girls disappeared, so all traces of the missing children, and any clues to their whereabouts or what happened to them, were erased underwater. Four children in total have disappeared, and detective Andrew Dalziel and his chief inspector Peter Pascoe investigate all the disappearances. An isolated, mentally disturbed fellow named Benny Lightfoot is suspected of murdering them, but Benny also disappeared after the flood and during the investigation of the first child disappearance.
However, a graffiti message about Benny's return appears, and the locals have reason to believe that Benny is still lurking around the area. Suddenly, Inspector Pascoe’s daughter becomes very ill, and she gets visions of a demonic water monster stealing the children. Elizabeth Wulfstan, another character, wants to make songs about dead children for the annual music festival of the town of Danby.
Despite Elizabeth's obsession with death, based on the clues in the story I believe she actually did not kill the three children who disappeared prior to the flooding of the town, even though this question suggests that Elizabeth did the killings. I believe the question is mistaken. I believe Elizabeth's father, Jack Allgood (Elizabeth's former name was Betsy Allgood), actually committed the killings of the three children. We learn from the clues in the story that he was attracted to young girls, and he molested and then killed the girls prior to the flooding. They were hidden up on Beulah Height. Jack secretly killed them to protect himself from being held responsible for molesting the young girls. Because I believe the question is mistaken, based on the clues in the story, I wanted to point that out and explain why.