Unhappy at event including daughter leading to feud (8)
I believe the answer is:
vendetta
'feud' is the definition.
(vendetta is a kind of feud)
'unhappy at event including daughter leading' is the wordplay.
'unhappy' is an anagram indicator.
'including' indicates putting letters inside.
'leading' indicates taking the first letters.
The initial letter of 'daughter' is 'd'.
'at'+'event'='atevent'
'atevent' anagrammed gives 'venetta'.
'venetta' going around 'd' is 'VENDETTA'.
'to' acts as a link.
(Other definitions for vendetta that I've seen before include "Violent quarrel" , "Family blood feud" , "Prolonged bitter quarrel" , "Violent feud" , "Lasting feud associated with Sicily and mafia" .)