Trouble had upset lovely thing in bed (6)
I believe the answer is:
dahlia
'lovely thing in bed' is the definition.
I can't judge whether this defines the answer.
'trouble had upset' is the wordplay.
'trouble' becomes 'ail' ('ail' can be a synonym of 'trouble').
'upset' says the letters should be written backwards.
'ail'+'had'='ailhad'
'ailhad' in reverse letter order is 'DAHLIA'.
Can you help me to learn more?
(Other definitions for dahlia that I've seen before include "Strangely, Ali had this flower" , "Flower genus" , "Showy garden plant" , "'Hi, a lad has the flower (6)'" , "Lia had this flower, strangely" .)