Don - I have in my file, Mary Faunce, born abt 1721-1728 and married to Joseph Allen on August 25, 1748.I have been unable to find anything at all regarding her parentage.
Joseph was born in Dartmouth and his daughter, Sarah (Allen) Wood was born and married in Dartmouth. First husband was Daniel Wood and second, Wanton Brightman of Dartmouth.
I have been able to find no parents for Mary - maybe she is a sister to your Margaret, the birthdates are close to each other.Do you have access to Dartmouth vital records? If not, I could take a look for you next time I go to the library.