One still has to ask what harm she has done. She has built nothing. A farmer could well install a pond, expecially if it helps with drainage, because this is simply caring for the land and using good husbandry.
I agree that council officials are people with a job to do, but we have probably all experienced bureaucracy at work - it is slow and inflexible. Regulations should be applied with sensitivity and respect for people as individuals,surely. There is also a possibility that the regulations should be changed if they lead to actions such as this, and this is ulikely to happen unless there is public pressure for it to happen.
I do think that most people find this decision puzzling and foolish. If it is against common sense, then people have the right to question it and to protest, in my view.