Hi AnnMarie,
It seems it was a bug. Earle-679 was linked twice as the daughter of Daniel Earle (Earle-775). That's why Mary was listed as her own sister.
I "removed Daniel Earle as the father from (one) Mary Earle" (this is what my contribution's log shows. This change is not listed on Earle-679 or Earle-775) and the problem was fixed.