As a singer, she's in Division One (4)
I believe the answer is:
diva
'division one' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'as a singer she's' is the wordplay.
I cannot really understand how this works, but
'a' is present in the answer.
'she' could be 'di' and 'di' is found within the answer.
A single letter 'v' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for diva that I've seen before include "Operatic ego" , "Distinguished female singer" , "Avid like opera singer" , "High-maintenace woman" , "Long narrow top" .)