The Mystery of "Lady Mary Grattan"

Facts known about Mary Grattan: 

• Was a "Lady"
• Born Nov 12, 1797
• Age 17 married Anthony Holt
• Had 6 children born in Ireland
• They came from Kilmeague at some point
• Emigrated to Canada in 1841
• Was known for possessing medical knowledge for the times (innoculated town in Canada using medical knowledge that could have been learned from medical journals circulating in Ireland from an English physician who developed the technology in 1798)

We (descendents and I) are trying to determine how or why she was a Lady. A professional genaologist many years ago gained insights from oral history, records, etc. A number of similar but conflicting stories create a possible theory, but there is no information about these facts below to confirm or deny the theories:

• She was a relation of a Dr. Richard Grattan MD with wife Grace of Carbury, Church of Ireland ?
• She was the possible dauhter or granddaughter of Lord Mayor of Dublin, Sir Richard Grattan 1735-1736 ?