Apparently, it is better to follow the logic proposed by teacher and find errors. Here, her logic of joing two circuits is perfectly correct but there is small mistake in implementation. She deserves much less disapproval than she's receiving.
In an apparent early modern example of urban legend, the invention of the pet door was attributed to Isaac Newton (1642–1727) in a story (authored anonymously and published in a column of anecdotes in 1893) to the effect that Newton foolishly made a large hole for his adult cat and a small one for her kittens, not realizing the kittens would follow the mother through the large one.