I wasn't able to locate a Mary Rosa, too many to figure out which one might be yours.
Interestingly, the 1920 census says she was born in Va and her parents were born in PA. 1910 says she and her parents were born in VA.
Sarah J.'s birth record lists her mother as Mary Ann M. Mitchell.
I could not find a marriage record for them
Have you gotten Mary's death certificate or checked the death records for Caroll Co.? You might also get her maiden name from the death certificates for Richard Clyde or her other children.