Lass, married, murdered brother (5)
I believe the answer is:
mabel
'lass' is the definition.
(I know that Mabel is a female given name)
'married murdered brother' is the wordplay.
'married' becomes 'm' (abbreviation, e.g. in genealogy).
'murdered brother' becomes 'abel' (Cain murdered Abel in the Bible).
'm'+'abel'='MABEL'
(Other definitions for mabel that I've seen before include "Lady" , "Girl" , "Mack's mate" , "Female name deriving from one meaning lovable" , "Female name; rhymes with mythic story" .)