Crossword Genius

Let fly, as good dressmakers should? (4,1,3)

Ross

I believe the answer is:

have a fit

'let fly' is the definition.
(both can mean to become very angry)

I don't understand how the remainder of the clue works.

(Other definitions for have a fit that I've seen before include "Become very angry" , "flare up" .)

I've seen this clue in The Guardian.
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