Susan cries out, dropping end of blue flower (9)
I believe the answer is:
Here is my best explanation:
'flower' is the definition.
I don't understand how the rest of the clue works.
(Other definitions for narcissus that I've seen before include "Self-centred youth", "In Greek myth, a lover of his own beauty", "Greek youth who fell in love with his own reflection", "Beautiful fellow", "Flower; Gk. youth in love with reflection", "Youth in love with own reflection", "Spring-flowering bulb", "Small daffodil", "Daffodil-like bulb" and "Spring flower".)