Girl at heart feels I embarrass her (5)
I believe the answer is:
elsie
'girl' is the definition.
'at heart feels i embarrass her' is the wordplay.
'at heart' says the answer is hidden in the clue (letters hidden in the heart of the clue).
'ELSIE' is hidden within 'feels i embarrass her'.
(Other definitions for elsie that I've seen before include "Lady" , "Girl's name" , "woman" , "Name for girl" , "Female name; rhymes with London football team" .)