Who is Mother Doig from This House of Sky: Landscapes of a Western Mind and what is their importance?

Mother Doig is Ivan's mother. She actually died early on in the boy's life. He was only 6 years old at the time. She had dark brown hair and asthma. Her parents were rather poor, but did the best they could with what they had. Her family made at least one major move in order to take her needs into account- this was their relocation to Montana.