Good queen supporting a British nun (6)
I believe the answer is:
abbess
'nun' is the definition.
(I have seen 'Superior nun ' mean 'abbess' so perhaps 'nun' could also mean 'abbess')
'good queen supporting a british' is the wordplay.
'good queen' becomes 'bess' (Good Queen Bess was a nickname of Elizabeth I).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'british' becomes 'b' (abbreviation e.g. in BBC).
'a'+'b'='ab'
'bess' put after 'ab' is 'ABBESS'.
(Other definitions for abbess that I've seen before include "Nun in charge of a monastery" , "Religious leader" , "Superior nun" , "Mother superior" , "Person in charge of convent" .)