I have just found some more information regarding Agnes CARSWELL that may be of some interest to you.
I found the birth reg for illegitimate daughter Janet Mitchell CARSWELL born Oct 1st 1877 but cannot find the birth reg for her son William or Wilhelm although I was able to find his marriage to Edith Christina BOWEN another relative of mine, in Manitou, Lisgar, MB on Nov 16 1908.
GROOM'S LAST NAME: CARSWELL GROOM'S GIVEN NAMES: WILLIAM
BRIDE'S LAST NAME: BOWEN BRIDE'S GIVEN NAMES: EDITH C DATE OF MARRIAGE: 11/16/1908
PLACE OF MARRIAGE: MANITOU REGISTRATION NUMBER: 1908,001033
With her husband Peter McMILLAN whom she married on Jan 8 1883, Agnes had the following children:
Annie Maria born Oct 15 1883 Marion May born Apr 8 1885 David Carswell born Mar 4 1887 Margaret born May 14 1889
Agnes died Jun 3 1889 in McNab Twp, Renfrew, Ontario, a few weeks after giving birth to her last child, Margaret and her death reg states that she died of heart disease 5 months.
I just moments ago discovered that Margaret born May 14 1889 was with her maternal grandfather David CARSWELL in 1901 Census in Pembina and she is listed with the exact date of birth and as Margaret CARSWELL.
Not sure why Margaret's father, Peter McMILLAN didn't raise Margaret and the others as his own since he married again to Sarah Ann GILLAN in 1890 and they had 1 daughter before Sarah died in 1892.
He married again a 3rd time to his daughter Annie Mary's mother-in-law, Annie Gertrude ROBERTS Eastwood and they were in Manitoba by 1904.
I would love to hear from you at your convenience.