I have a Margaret Johnson married to William Beatty (born 1823) of Country Cavan Ireland in my family tree. I don't have any specific information on Margaret other than she was also from County Cavan and her son George Beatty (Born 1851) married Jane Montgomery. Jane and George eventually came to Canada. My family records indicate that William Beatty joined his son and daughter-in-law in Canada alone. I can only assume that Margaret died in Ireland.
Could this be the same Margaret Johnson you are looking for?