Information on Surname of Dunn

I have been researching on Surname of Dunn, it seem that I am not able to locate its connection between Dunn and Minkler.

My grandmother, Dorothy Ann Minkler, her parent is Allen Orange Minkler and Mary Dunn. It is quietly hard for me to find those information on Mary Dunn, my great-grandmother.

If you have information on those, it would be very helpful to my research project if you would provide me some information related to my great-grandmother, Mary Dunn.