Flower girl likely to lose heart (4)
I believe the answer is:
lily
'flower girl' is the definition.
(I've seen this in other clues)
'likely to lose heart' is the wordplay.
'to lose heart' suggests removing the centre (I've seen 'lost heart' mean this).
'likely' with its centre removed is 'LILY'.
(Other definitions for lily that I've seen before include "Bulb with showy, typically pendulous flowers" , "Flower, maybe of the valley" , "Fleur-de-lis" , "Trumpet-shaped flowering plant" , "Bulbous flowering plant" .)