Briar, 12, swam out into the water first, to check there were no logs in the way.
She managed the drop from the swing without difficulty. After jumping twice she said it was fun.
But when her older sister Samantha tried she emerged from the water in intense pain. She had hit the sandy riverbed with her feet. Wyley rang for an ambulance and Samantha was taken to Whanganui Hospital.
She was found to have fractured one ankle in two places. She was in hospital overnight, had surgery and now has screws holding her bones together.
She will spend six weeks in plaster.
A staff member at the hospital told Wyley Samantha was "about the sixth" accident they had had this summer from Mosquito Point.
Wyley is glad the swing has been put back, because she says children need to learn about risk.
But she wonders whether that swing is really too risky.
A hospital spokesman was unable to say exactly how many accidents have happened at Mosquito Point since Whanganui District Council reinstated the swing in early December.
An ACC spokesman was similarly unable to give definite numbers.
"The info we get on accident descriptions is entirely down to the claimant, and it is questionable how many of them would be specific enough to identify Mosquito Point as the site of their accident."
Trudy Taylor, who was a station manager and paramedic for St John Ambulance in Whanganui for 18 years, has been to many accidents at Mosquito Point.
"I have certainly been to some real doozies up there, people breaking bones and that sort of thing. But we also go to Kowhai Park and pick up people that have fallen off things," she said.
Whanganui District Council has been approached for comment.