Hello,
A Margaret McGuffie was my maternal great-great grandmother, provided we are speaking of the same person.
The information at my disposal is that she was born in 1835 in Kirkinner, which is just to the east of "The Whaup", (or Whauphill), whereas Glasserton is down on the coast road from the Port to Whithorn. However, I have no attestation for my info, and my family has agricultural links to the area going back generations, so I'd be intersted to know where your link to "Glasserton" comes from. The family farm was at Barrachan (Shed Park or "Shedlach of Barrachan"). In the 1851 census, she is stated as age 18, which may make her birth date 1833. Parents John and Marion McGuffie. Married Henry Dixon (b. NI 1829, died 1879).
Same person?