Agitated girl with unusually neat figure (8)

I believe the answer is:

triangle

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'figure' is the definition.
(triangle is a kind of figure)

I can't explain the rest of the clue.

(Other definitions for triangle that I've seen before include "Percussion instrument of geometric origin" , "Simple percussion instrument" , "Alerting (anag)" , "involved in eternal emotional conflict" , "Figure - percussion instrument" .)

I've seen this clue in The Globe and Mail.

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