When I say "certificate", I mean a church record or other supporting document - because I'm looking for her maiden name and trying to trace any details.
When she married William E. Winchell, her name was 'Cooper' and she had children from a previous marriage. The 1840 census shows Margaret Cooper as head of household, living in Grove, NY with children. I found a William E. Winchell who lived in West Bloomfield, Ontario County, NY who could be the man she married.
In 1850, Margaret was married to William E. Winchell and they were living in Burton, Cattaraugus County with her children and his. The 1855 state census gives William E. Winchell's place of birth as Cayuga County, 57 years old and had lived in Allegany County for 6 years. In 1860, they are living in Amity, NY.