I am also researching this just now and believe the Young surname is uncertain. The original source of the information in a 1998 forum backed out, saying it was from memory and she had destroyed the notes. There was a Sarah Dendy Young, daughter-in-law to John Dendy's uncle, Thomas. So there may have been confusion there. On the other hand, it would be common for Dendy-Young marriage to be accompanied by a Young-Dendy marriage in the same area, so the Young name is very possible.
Whatever her birth name, she was probably mtdna haplogroup T2, HVR1 16126C 16294T 16296T 16304C 16519C, lineage probably from southeast England...
3 Mar 1800
Probate of Thomas Dendys will, originally dated 20 Sep 1799. Names wife Mary. Children: Elizabeth Powell (wife of Samuel), Sarah Young (wife of James), Patsy Walker (wife of Harmon), Cornelius, Thomas, William.
Exr.: Mary (wife) and William (son). Wit.: John Hunter, William Dendy, Samuel (X) Leak