I have a Philomene Poitras who was the daughter of David Poitras and Marie Seraphine Dutremble dit Desrosiers.She was one of nine children born this couple.
David Poitras was the son of Gabriel Poitras who was born about 1784 in L'Islet Quebec.He married Marie Chasse who was born about 1790 in St-Louis de Kamouraska, Quebec.
The Poitras line back to Laurent Poitras (as far back as anyone has gone at this time) is Philomene; David; Gabriel; Pierre; Michel; Joseph Lucien; Jean; Laurent.
I don't know if this is your Philomene, but the dates and places seem to suggest it might be.
I know of a book that contains several thousand Poitras descendents from Jean and Marie-Xainte Vivier.
This book traces the descendents of Jean Poitras and Marie-Xainte Vivier through their son, Joseph-Lucien Poitras; Joseph's son Michel Poitras; Michel's son Pierre Poitras; and Pierre's son Gabriel Poitras. Gabriel married Marie Chasse at St-Andre-de-Kamouraska, Quebec, on 19 Jul 1813.
Below is the information on this book which I understand is out of print. But I know there are copies available at certain libraries (in Quebec archives as well).
Title: Repertoire genealogique des Poitras du Madawaska By: Leo Poitras and Jean-Guy Poitras
(Catalog No. US/CAN 929.271 P756p; LDS Family History Library, Salt Lake City, UT)
The lead-in paragraph reads: Les Poitas du Madawaska descendent de Gabriel Poitras dont les enfants s'installent en terre madawaskayenne il ye a cent cinquante ans. Voici la ligne directe de Gabriel Poitras a partir de jean Poitras, premier ancetre debarque en Amerique.
Again, if this is your Philomene (which the above book will tell you), then you have just found a gold mine!Good luck!