Girl found over in Hammersmith (4)
I believe the answer is:
emma
'girl' is the definition.
'found over in hammersmith' is the wordplay.
'over' is a reversal indicator.
'found' indicates the answer is hidden within the clue.
'amme' is hidden within 'in hammersmith'.
'amme' backwards is 'EMMA'.
(Other definitions for emma that I've seen before include "Ack -, a term for a.m." , "Mrs Bovary" , "Jane Austen novel and Nelson's lover" , "Eponymous heroine" , "Jane Austen heroine" .)