Girl whos out of breath (6)

I believe the answer is:

bertha

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'girl' is the definition.

'whos out of breath' is the wordplay.
'breath' anagrams to 'BERTHA'.
Though, I'm unsure how this is indicated.

(Other definitions for bertha that I've seen before include "collar" , "The bar (anag.)" , "Woman's name" , "Big - - , WW1 gun" , "Big girl" .)

I've seen this clue in The Irish Independent.

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