Maria not unhappy with a lover (9)
I believe the answer is:
inamorata
'lover' is the definition.
(thesaurus)
'maria not unhappy with a' is the wordplay.
'unhappy with' is an anagram indicator.
'maria'+'not'='marianot'
'marianot' anagrammed with 'a' gives 'INAMORATA'.
(Other definitions for inamorata that I've seen before include "Girlfriend" , "6 across [BOSOM] friend" , "loved one" , "Sweetheart" , "Beloved of one another" .)