Her singing is the end (3,4)

I believe the answer is:

fat lady

If this is the answer I cannot explain how the clue works.

(Other definitions for fat lady that I've seen before include "Tubby diva" , "` `The opera ain't over till the ... .... sings' '" , "''The opera ain't over til the ....... sings''" , "She must sing before the show ends" .)

I've seen this clue in The Guardian.

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