Dame Elizabeth Chaplin who married Charles Gregory is strictly speaking given the wrong title - she should have been Lady.
However, as I said before in times past, it was not as fixed as it is now. I have the widow of a knight who died in the 16th century who was referred to as Dame Elizabeth - strictly speaking she was Lady. Another in the mid 17th century, also referred to as Dame. Perhaps it comes from the custom of listing them in the will calendars in Latin? Dominus for the knight, title Sir and Domina for the knight's wife, interpreted as Dame, (instead of Lady) which is probably a contraction of Domina. Some clerks grasp of Latin was better than others.
Nell