She's orderly, but doesn't take orders (3)

I believe the answer is:

nun

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'she's' is the definition.
Both the definition and answer are singular nouns.
Maybe they are linked in a way I don't understand?

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for nun that I've seen before include "Mother Superior, perhaps" , "Woman with a habit" , "whose son entered Promised Land" , "Mother Teresa, maybe" , "Woman in religious order" .)

I've seen this clue in the Evening Standard.

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