Of course the copy for "The Rogue's Wallet" mentions George's name! Right before the line, "He killed my mother," is a line which says, "His name was Costanza." Last time I looked, George's last name was Costanza!
Also, just because George did not kill ELAINE'S mother doesn't mean she can't write the copy for the wallet. Creative writers can write about ANYTHING! Novelists, playwrights and screenwriters (even "Seinfeld" writers) write about things that are not in their experiences in the first person when necessary. Peterman could have TOLD Elaine his concept and she could have come up with the copy. Peterman is "The Big Cheese." "Big Cheeses" usually hire other people (like Elaine) to do the day-to-day work while they run the higher levels of the business. Why would Peterman hire Elaine to write copy if he was writing copy himself? He could simply save the money.