After Nia had watered the seedlings, she had locked the shed and had cycled home.✓Correct answer
The lights came on, the audience found their seats and the concert began.
By the time the vet arrived, the farmer had moved the calf into a warm stall.
Dylan remembered that he had saved the receipt in a desk drawer.
Explanation
The allotment sentence unnecessarily keeps the past perfect for a simple succession of completed jobs. The other sentences either use the past simple for ordered events or use one past perfect to mark an event earlier than a later past reference point.