Answer:
Sometimes, Imitation is bad but sometimes it isnt bad at all. It may help the child understand and distinguish the right from the wrong like being polite from being immature... And when Hellen imitated Sullivan's hand gestures, she didnt notice that she was spelling a word in the same time and she didnt know that words existed and that people are talking one language at the same time.
So, in the book, her imitation isn't bad at all.