Weakens, but keeps her wits about her! (7)

I believe the answer is:

withers

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'weakens but keeps her' is the definition.
I can't judge whether this definition defines the answer.

'wits about her' is the wordplay.
'about' means one lot of letters goes inside another.
'wits' enclosing 'her' is 'WITHERS'.

Can you help me to learn more?

(Other definitions for withers that I've seen before include "Part of bay for example" , "Highest part of horse's back" , "droops?" , "Bit of a nag" , "Shrivels" .)

I've seen this clue in the Evening Standard.

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