Where she's concerned, I'm wrong again (4)
I believe the answer is:
mimi
'where she's concerned' is the definition.
The definition suggests a singular noun which matches the answer.
'i'm wrong again' is the wordplay.
'wrong' is an anagram indicator.
'again' becomes 'mi' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'im' is an anagram of 'mi'.
'mi'+'mi'='MIMI'
Can you help me to learn more?
(Other definitions for mimi that I've seen before include "I'm upset twice by the operatic girl" , "La Boheme character (whose tiny hand is frozen)" , "I'm, I'm mad about the heroine in 'La Boheme'" , "'They call me - - ' , (Lucia)" , "Tragic heroine" .)