Trouble follows an enormous girl (7)
I believe the answer is:
abigail
'girl' is the definition.
'trouble follows an enormous' is the wordplay.
'trouble' becomes 'ail' (synonyms).
'follows' means one lot of letters go next to another.
'an' becomes 'a'.
'enormous' becomes 'big' (similar in meaning).
'a'+'big'='abig'
'ail' after 'abig' is 'ABIGAIL'.
(Other definitions for abigail that I've seen before include "lady!" , "Lady's maid (once); David's wife (I. Sam.)" , "domestic" , "Woman" , "She served David" .)