She was added during script revisions.
"Cain needs a love interest," said Stan, leaning back, surveying the room for approval.
Heather and Mort pondered Stan's suggestion for a moment. It wasn't the worst idea they'd heard, and it was getting late.
Mort broke the silence. "Yeah, definitely. But someone with edge. We're talkin' Old Testament here -- y'know, stonings, plagues and shit."
Heather sat forward. "Right! Like, say, his sister!"
"Brilliant!" yelled Stan. "That's Old School Testament!"
"If we're going the incest route," said Mort, "then let's go all the way. Cain marries his *twin* sister."
Everyone smiled.
"Ka-ching!" said Stan.
DP