Have you looked into the possibility that Elizabeth (Betsy) Turner was the grand daughter of HBC surveyor Phillip Turnor?
Her age would be right, although census irregularities put has a born either 1818-19 or 1826 and not the 1823 documented elsewhere. HBC bio says her father Jospeh Sr. was working in the Lake Superior area in early-mid 1840s When she could have met Chas Roussain, and the 1871 census shows a sister Mathilda Turner living with her. Mathilda's age on the census corresponds to documentation of Jospeh's daughter Mathilda.
Just something to look into.