She's in egg production (3)
I believe the answer is:
hen
This clue might be a double definition.
'she's' is the first definition.
Both the answer and definition are singular nouns.
Maybe there's an association between them I don't understand?
'egg production' is the second definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'in' acts as a link.
Can you help me to learn more?
(Other definitions for hen that I've seen before include "Domestic fowl" , "Domestic egg layer" , "This party is for women only" , "Not cock" , "Clucking female" .)