Alice Amanda Flagg's parents

Judson Losee was married to Alice Flagg, who was born in Quebec. According to the 1870 US Census, Alice was born around 1851.

For a long time, on our genealogical records her mother was listed as Mary Ann Derick. However, Mary Ann Derick died in 1848. At the time of the US Census in 1870, Alice's father, Isaac Flagg, was still listed as being married to a woman named Mary. Was this Mary Ann Derick, and her date of death was recorded incorrectly?

It turns out that after his first wife died in 1848, Isaac Flagg remarried a woman named Mary Pier in 1850. Unfortunately, we have no information about Mary Pier's ancestry at this time.

But here's an electronic version of the record of the marriage between Isaac Flagg and Mary Pier:

From the registers of the Anglican Church serving
St. Armand East, Quebec (now called Frelighsburg), register for
the year 1849 on the front of folio 21, Quebec National Archives
microfilm #124.4:

On this ninteenth day of March one thousand eight hundred and
fifty Isaac Flagg, widower, of the Parish of St. Thomas, Farmer,
andMary Pier of this Parish, spinster, both of major age, were
married by dispensation of Licence bearing date the fourteenth day
of the present month of Marchin presence of John Pier Jr. and
Abby A. Pier both of this Parish, who hereunto set and subscribed
their names by me
(signed) James Reid, Rector
(signed)
Isaac Flagg
Mary Pier
John Peer Jr.
Abby A. Peer

Source. Notice how Pier is also spelled "Peer" by the clergyman. Were John Peer and Abby Peer the parents of Mary Pier?

And here's a link to the diary of the clergyman who married them, where he records, on March 19, 1850, "I married a man of the name of Isaac Flagg, of St. Thomas, and Mary Pier today."

UPDATE: According to the 1861 Canada Census, John and Abby Peer were married, but not old enough to have been Mary's parents. Perhaps John was Mary's brother?

UPDATE 2: Here's a copy of the recording by the clergyman: