Diane's flower is a complete failure (8)
I believe the answer is:
disaster
'a complete failure' is the definition.
(I've seen this before)
'diane's flower' is the wordplay.
'diane's' becomes 'di's' (short for Diane).
'flower' becomes 'aster' (type of flower).
'dis'+'aster'='DISASTER'
'is' acts as a link.
(Other definitions for disaster that I've seen before include "Event causing great damage" , "Catastrophic occurrence" , "Calamity, sudden great misfortune" , "terrible trouble" , "Sudden catastrophe" .)