Stringed instrument initially captivated a girl (7)
I believe the answer is:
rebecca
'girl' is the definition.
(girl's name)
'stringed instrument initially captivated a' is the wordplay.
'stringed instrument' becomes 'rebec' (I've seen this in another clue).
'initially' suggests taking the first letters.
The initial letter of 'captivated' is 'c'.
'rebec'+'c'+'a'='REBECCA'
(Other definitions for rebecca that I've seen before include "Daphne du Maurier book; girl's name" , "1938 novel, starting: 'Last night I dreamt I went to Manderley again'" , "Daphne du Maurier's antiheroine" , "also Isaac" , "Literary heroine" .)