Diana's edge initially disheartened the vulnerable (13)
I believe the answer is:
disadvantaged
'vulnerable' is the definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I don't see?
'diana's edge initially disheartened' is the wordplay.
'diana's' becomes 'Di's' (Di is short for Diana).
'edge' becomes 'advantage' (I've seen this before).
'initially disheartened' becomes 'd' (I can't justify this - if you can you should believe this answer much more).
'dis'+'advantage'+'d'='DISADVANTAGED'
'the' is the link.
Can you help me to learn more?
(Other definitions for disadvantaged that I've seen before include "In unfavourable circumstances" , "Put in an unfavourable position" , "In deprived circumstances" , "Socially or economically deprived" , "Handicapped" .)