After the death of Agatha's father, her mother married Joseph Bailly, a fur trader of French descent originally from Nova Scotia who came to some prominence.

Agatha and her mother were recorded by contemporary Elisabeth Baird as wearing the traditional dress of the Métis women of the area at the wedding.

[10][8] Their youngest daughter Mary died at the age of eight after falling through the ice while travelling between Mackinac Island and St. Ignace and her grave is the oldest in the St. Ann cemetery.

[10] During the early period of the fur trade the Mackinac and surrounded area were primarily inhabited by First Nations people, but by the middle of the nineteenth century their numbers were greatly reduced due to war, including the War of 1812, and treaties which saw many of the local Ojibwe and Odawa people relocated to tiny parcels of land.

Biddle took on a number of community roles, including taking in sick or orphaned Anishnaabe children and offering food and other charity.