Female monarch in swirling bath (6)

I believe the answer is:

bertha

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

'monarch in swirling bath' is the wordplay.
'monarch' becomes 'ER' (abbreviation for Elizabeth Regina, British Queen).
'in' indicates putting letters inside.
'swirling' indicates an anagram.
'bath' is an anagram of 'btha'.
'er' put within 'btha' is 'BERTHA'.

Can you help me to learn more?

(Other definitions for bertha that I've seen before include "Girl's name - big German WWI gun" , "Big girl" , "big woman?" , "Breath (anag) - girl's name" , "The bar (anag.)" .)

I've seen this clue in The Sun.

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