If not a dunderhead, she could be a honey! (6)
I believe the answer is:
hoyden
'if not a' is the definition.
I can't tell whether this defines the answer.
'dunderhead she could be a honey' is the wordplay.
I cannot quite understand how this works, but
'dunderhead' could be 'd' (head letter of 'dunder') and 'd' is present in the answer.
an anagram of 'honey' is 'hoyen' which is present in the left over letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for hoyden that I've seen before include "Reliable (convict)" , "A girl who behaves in a boyish manner" , "A boisterous girl" , "Romp" , "No Hyde (anag)" .)