Go to the county Board of Elections, ID yourself, explain the problem and request the voting records for the time period in question. They may ask you to fill out a FOIA request. If they try to deny you access, have them put the denial in writing and take it to your state representative or U.S. Congressman.
I have a question.
If grandma was a resident of NYS, could her name be used as a voter in FLA or some other State? Is there a way of finding out if grandma is voting anywhere in the USA - after she passed away?