Emphasis with Diana in pain (8)
I believe the answer is:
distress
'pain' is the definition.
(I know that distress is a type of pain)
'emphasis with diana' is the wordplay.
'emphasis' becomes 'stress' (stress is a kind of emphasis).
'with' means one lot of letters go next to another.
'diana' becomes 'di' (Di is short for Diana).
'stress' after 'di' is 'DISTRESS'.
'in' acts as a link.
(Other definitions for distress that I've seen before include "Affliction" , "Sadden" , "Mental or emotional pain" , "Misery" , "Peril" .)