Sounds to me like your grandmother's surname may have been Saint Amand (or one of the close sounding St's). If she was at all French and or from Canada, she probably had it changed in the late 1800's from Saint Amand.
Start looking in the census for names that sound close to it...forget the spelling, just go with the sound. It helps if you know her ethnicity. Once you find someone in the latest census for which they were alive, it will open up the doors.