The best starting point for questions of this type is generally the published vital records for a town. Those for Dartmouth are in the public domain and can be freely downloaded online.
It is unlikely that she was born in Dartmouth. That town was not mentioned in New Plymouth Colony records until 03-Oct-1652, and the the town records, as published, contain no record of her birth. The is also no record of her death and no gravestone record in the published records.
The surname of the wife of the younger William Macomber of Marshfield is, as far as I can determine. not known, Her given name was Mary, and she was named in her husband's 1711 will. I find no contemporary record that would provide her surname, and I find no surname for her in secondary sources for the Macomber and Randall families.
Dale H. Cook, Member, NEHGS and MA Society of Mayflower Descendants;
Plymouth Co. MA Coordinator for the USGenWeb Project
Administrator of http://plymouthcolony.net