I am not a descendant of Rebecca - but do have information on her line and her husband Henry's line. Both are descended from Thomas Dow of Ipswich (a son of Henry Dow of England who came to Watertown MA in 1637). Rebecca was the grandaughter of Thomas's son Ebenezer (b. 1692); Henry was the grandson of Thomas's son Thomas (b.1694). That would make them 2nd cousins.