Taking most of bed, the fat lady? (4)
I believe the answer is:
diva
'fat lady?' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for diva that I've seen before include "Great performer" , "High-maintenance opera singer?" , "Callas, say" , "Long narrow top" , "Operatic soprano" .)