Spoil good American girl with cocktail (9)
I believe the answer is:
margarita
'cocktail' is the definition.
(margarita is a kind of cocktail)
'spoil good american girl' is the wordplay.
'spoil' becomes 'mar' (I've seen this before).
'good' becomes 'g' (abbreviation).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'girl' becomes 'rita' (**).
'mar'+'g'+'a'+'rita'='MARGARITA'
'with' acts as a link.
(Other definitions for margarita that I've seen before include "Cocktail consisting of tequila and lemon juice" , "Stiff drink" , "Tequila and lime cocktail" , "Tequila/citrus cocktail" , "Tequila-based cocktail" .)