Carmela was murdered along with her Husband Franco Bertinelli and several other family members by
Omerta the Silencer on the order of Stefano Mandragora. It is this that causes her daughter Helena to become the Huntress. She was carrying on an affair with Santo Cassamento, the don of a rival mafia family.
DC Animated Universe / Justice League Unlimited
Carmela's daughter Helena was an adult when Carmela was killed but in the cartoon Justice League Unlimited she was a little girl. Another difference between the comic and the cartoon was they were actually killed by Mandragora and not the Silencer.