Camille is upset about an unsuitable marriage (11)
I believe the answer is:
misalliance
'unsuitable marriage' is the definition.
(I've seen this before)
'camille is upset about an' is the wordplay.
'upset' is an anagram indicator.
'about' is an insertion indicator.
'camille'+'is'='camilleis'
'camilleis' anagrammed gives 'misallice'.
'misallice' going around 'an' is 'MISALLIANCE'.
(Other definitions for misalliance that I've seen before include "result of poor choice of partner" , "Unsuitable marriage" , "Squabbling partners" .)