I've been looking for evidence to confirm that her birth name was "Plummer" and I cannot find any. She was NOT daughter to Thomas and Elizabeth Plummer of Nottinghamshire, England - he was dead by mid-1761.
She's listed on her husband Dominicus Gray's tombstone as just "Sarah" (not "Sally"), no birth date, death date still fairly legible.
IF she's a Plummer at all, she is likely to be a Massachusetts Plummer.
(Incidentally, BEWARE: there were at least two Dominicus Grays in Vermont, one in Groton, one in Arington. They were probably not related, as Dominicus Gray of Arlington seems to have belonged to a family that moved up from Connecticut.)