Young girl making a mess of neater clothes, say, being contrarian (8)

I believe the answer is:

teenager

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But I can't explain it at all! Could you help me understand?

(Other definitions for teenager that I've seen before include "Youngster" , "Old child or young adult?" , "Young person" , "troublesome youth" , "Generate (anag)" .)

I've seen this clue in The Hindu.

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