I knew that I had found the right person because the record had been filled in by my grandfather William Matthew Todd, her son. The details were fabulous on this record. Grandmother Margaret was born 18th of November 1863 and she died at the age of 75 years, 5 months and 1 day. Her death was caused by chronic endocarditis. (It causes an infection of the heart valve which in turn causes the heart to be ineffective in pumping blood through the body). A wonderful find on this record was the name of her parents, John McClenahan and Margaret Marrs. Unfortunately they are listed as born in Ireland. It is challenging to locate Irish records without more details.
Never give up when you are researching. Most research sites have Soundex which indexes names by sound. An example is the name Claire. It has two alternatives, Clare/Clair, which are both pronounced the same. Searching for one spelling wouldn't show results for the two others. As with most research it is always in the details!