She’s a girl madly in love? Quite the opposite! (6)
I believe the answer is:
gloria
'love? quite the opposite' is the definition.
I can't tell whether this defines the answer.
'she's a girl madly in' is the wordplay.
'she' becomes 'lori' ().
'girl' becomes 'g'.
'madly' is an anagram indicator.
'in' means one lot of letters goes inside another.
'a'+'g'='ag'
'ag' anagrammed gives 'ga'.
'lori' put into 'ga' is 'GLORIA'.
Can you help me to learn more?
(Other definitions for gloria that I've seen before include "Part of the Mass; name" , "Prayer: '... in excelsis Deo'" , "Hymn of praise" , "sung in church" , "Oil rag for a girl" .)