It took a very long time to discovery her roots, but those came pouring in like an avalanche several months ago when I discovered my very distant cousin, Jonathan Tetreault's work online. He linked Garrow to Mace/Masse, which I knew existed but was unable to piece together.
Jonathan also found for me my 3GRGR's baptismal record. The copy available on ancestry.com is pretty weak. So, I found a much higher res version today on Family Search -- thanks again, Mormons.
Jonathan was also good enough to translate it entirely for me:
March 20, 1817, by the undersigned priest baptized Marie Geneviève, born the 18th of the same month, of the legitimate marriage of Joseph Garant, day laborer in this parish, and Geneviève Mâcé. The godfather was Pierre Mâcé and godmother Geneviève Lanier, who didn't sign, also the father was present."Jane Garrow" was one of 17 children to Joseph Garant and Sylvia Genevieve Mace. The connection that I knew about and that eventually lead me to Jonathan and this flood of information was that Jane's mother's brother (her uncle) was named Moss or Masse and had a daughter Emily, who my 3GRGR took as his second wife.
Jane's grandfather / godfather, Pierre Masse had another daughter (Jane's aunt) Marie Agathe Mace (b. 1793), who married Jean Baptiste LaPorte (b. 1784) , who is also responsible for a slew of LaPortes in the North Country.