When the death certificate is filled out, the family member or the clerk could have put the wrong name down as the mother, by mistake. It has happened. I would go with the census. My father put his grandfather down as Malvery and it was Mallory. And there was a Malvery as well as Mallory. He didn't know his father's family that well, because they didn't keep in touch with them. He was trying to fill in the death certificate buy memory from childhood.