Girl composed verse full of ecstasy (9)
I believe the answer is:
madeleine
'girl' is the definition.
(madeleine matches up with the definition girl)
'composed verse full of ecstasy' is the wordplay.
'composed' becomes 'made'.
'verse' becomes 'line' (I've seen this in another clue).
'full of' indicates putting letters inside.
'ecstasy' becomes 'E' (informal term for the drug).
'line' enclosing 'e' is 'leine'.
'made'+'leine'='MADELEINE'
(Other definitions for madeleine that I've seen before include "Small sponge cake" , "Item on sweet menu" , "Woman" .)