There are several User submitted Ancestral Files on familysearch.org. Several indicate her parents were John Pierce and Ruth Bishop. This first one has more extensive lineage but you may want to check several others to look for more details.
https://familysearch.org/pal:/MM9.2.1/SP7S-HM7
Others grouped at:
https://familysearch.org/search/tree/results#count=20&query=%2Bgivenname%3Arebecca~%20%2Bsurname%3Apierce~%20%2Bbirth_place%3AMe~%20%2Bbirth_year%3A1695-1705~
You might also want to look at these 2 texts that include the lineage of Anthony > John and Ruth Pierce > Rebecca. They may be the sources for the pedigrees in the previous answer related to the User Submitted Ancestral Trees.
New England Families, Genealogical and Memorial: A Record of the Achievements of Her People in the Making of Commonwealths and the Founding of a Nation, Volume 4
By William Richard Cutter
http://books.google.com/books?id=NfksAAAAYAAJ&pg=PA1853&lpg=PA1853&dq=ruth+bishop:john+pierce&source=bl&ots=mIN6sKrCwo&sig=V_08a2iwsl-S6DYIeKeTvFsFoP0&hl=en&sa=X&ei=bZGBUfptiPPSAbWHgcgI&sqi=2&ved=0CC0Q6AEwAA#v=onepage&q=ruth%20bishop%3Ajohn%20pierce&f=false
Pierce genealogy, being the record of the posterity of John Pers, an early inhabitant of Watertown, in New England by Frederick Clifton Pierce
http://archive.org/stream/peircegenealogy00piergoog#page/n0/mode/2up