She's good - none can imitate her (3)
I believe the answer is:
nun
'she's' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see a link between them that I don't see?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for nun that I've seen before include "Domestic fancy pigeon" , "Woman in Holy Orders" , "A palindromic lady in religious order" , "Fancy pigeon variety" , "Convent dweller" .)