Margaret is daughter of Joseph South.
Peter and Margaret (South) VanNote are listed as heirs of Joseph South in 1848. In the 1850 census there was a Dillon child living with Peter & Margaret, the daughter of Margaret's sister, Priscilla (South) Dillon.
Children of Joseph South mentioned as heirs in his 1848 estate:
Randall Dillon and Priscilla South, his wife (name also seen as Randolph)
Benjamin Skillman and Hannah South, his wife
Azariah Reed amd Rebecca South, his wife
Daniel South and Sarah Ann Pearson, his wife
Peter VanNote and Margaret South, his wife
Joseph South and Caroline Everingham, his wife
William Cornish married Mary South, who was dead by 1848 when the estate was divided. Mary (South) had two children -- Hannah and William who married Hannah Montgomery. She is buried in a single grave in Greenwood Cem, Hamilton Twp, Mercer Co, NJ. William signed her death certificate and just seems to have disappeared. Fact is daughter Hannah and brother William seem to vanish.