She plays with a key in a lock (7)
I believe the answer is:
actress
'she plays with a' is the definition.
I can't judge whether this defines the answer.
'key in a lock' is the wordplay.
'key' becomes 'c' (musical key).
'in' indicates putting letters inside.
'lock' becomes 'tress' (both can mean a piece of hair).
'a'+'tress'='atress'
'c' put inside 'atress' is 'ACTRESS'.
Can you help me to learn more?
(Other definitions for actress that I've seen before include "Female thespian" , "Female performer" , "Female player" , "eg Emma Thompson" , "One playing" .)