I wonder if this debate lies with the age of the sponsor. When I was young sponsorship was never paid up front, the deed had to be done and whoever had been sponsored proudly came round to say they had completed the task and were duly paid.
These days I guess everyone is more affluent and 'it's...
That is not the point, if she had come back after and said she had only done 4 miles I'm sure she would have still got the 5 pounds, the OP never objected to the payment.
The principle is paying the sponsorship after doing / attempting to do the task, otherwise why bother having a task or...