Flower in her arrangement (5)
I believe the answer is:
rhine
'flower' is the definition.
(River Rhine, something which flows)
'in her arrangement' is the wordplay.
'arrangement' indicates anagramming the letters.
'in'+'her'='inher'
'inher' with letters rearranged gives 'RHINE'.
(Other definitions for rhine that I've seen before include "Cologne's river" , "water" , "Ring river (Wagner)" , "Great European river with Lorelei Rock" , "fed by 8 [RHUR]" .)