Emphasised being upset -- not Diana! (8)
I believe the answer is:
stressed
'emphasised' is the definition.
('stress' can be a synonym of 'emphasize')
'being upset not diana' is the wordplay.
I cannot quite understand how this works, but
'being' could be 'esse' (I've seen this in other clues) and 'esse' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stressed that I've seen before include "under force" , "Insisted" , "Suffering from physical or emotional strain" , "on edge" , "Placed emphasis on" .)