Being gay, the girl hated to be different (5-7)
I believe the answer is:
light-hearted
'being gay' is the definition.
'the girl hated to be different' is the wordplay.
'to be different' indicates an anagram (I've seen 'is different' mean this).
'the'+'girl'+'hated'='thegirlhated'
'thegirlhated' with letters rearranged gives 'LIGHT-HEARTED'.
(Other definitions for light-hearted that I've seen before include "Cheerful, unserious" , "Playful" , "Amusing, entertaining" , "Cheerful, carefree" , "Happy-go-lucky" .)