In different ways, a girl is moony (5)
I believe the answer is:
lunar
'moony' is the definition.
(I've seen this in another clue)
'in different ways a girl' is the wordplay.
'in' means one lot of letters goes inside another.
'different ways' becomes 'lr' (I can't explain this - if you can you should believe this answer much more).
'a girl' becomes 'Una' (girl's name).
'lr' enclosing 'una' is 'LUNAR'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for lunar that I've seen before include "Belonging to the moon" , "Appertaining to the moon" , "that could describe landscape with more than one mare" , "Of a natural satellite" , "Kind of eclipse" .)