Jenny, a little like Robin (4)

I believe the answer is:

wren

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'jenny' is the definition.
(jenny wren is another name for a wren)

I can't explain the remainder of the clue.

(Other definitions for wren that I've seen before include "Bird - former British servicewoman" , "Tiny brown songbird with short erect tail" , "She served" , "Farthing's emblem" , "serving girl" .)

I've seen this clue in the Evening Standard.

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