Her mate's a real show-off! (6)
I believe the answer is:
peahen
'show-off' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for peahen that I've seen before include "Drabber female of a spectacular bird" , "Female fowl with a resplendent mate" , "Drab bird" , "Female bird (with a proud partner?)" , "Female of the large bird, Pavo species" .)