What is the role of disease in Tracks, and how does this relate to Peter Barry's postcolonial theme of "double or hybrid identity"? How are these divided identities represented in Tracks?

In the novel, disease highlights the fracturing of the Ojibwe identity. Peter Barry describes this process of fragmentation in terms of hybridization or duality.
The role of disease is two-fold: Erdrich draws attention to the fragmenting nature of disease on both a macro and micro level. At the macro level, disease threatens the viability of the entire Ojibwe societal structure. At the micro level, disease is a metaphor for the conflicting duality that epitomizes the post-colonial Ojibwe experience.
Peter Barry asserts that the post-colonial experience encapsulates the journey to overcome this hybridity. The first stage describes the "Adopt" stage, where the native mind absorbs European norms as universally relevant. The second stage describes the "Adapt" stage, where the native mind adapts European values to native suppositions. The last stage is the "Adept" stage, where the native mind has achieved full independence from colonial philosophical constructs.
Through Nanapush's story, Erdrich highlights the infectious diseases European civilization brought to native American shores. Although diseases such as small pox, cholera, mumps, and tuberculosis were not necessarily fatal to Europeans, these diseases caused widespread deaths among tribes like the Ojibwe (Chippewa). However, in his characteristic Native American humor, Nanapush describes himself as the "trickster" who managed to cheat death through his loquaciousness. His character is juxtaposed against that of Pauline, who struggles to reconcile her Ojibwe identity with her post-colonial inclinations.
At the micro level, Pauline is "sick." Of mixed blood, Pauline tries to replace her tribal ethics for European conceptions of purity. She frets that all Natives are invisible to Europeans and begins to believe that European civilization is superior, both philosophically and politically. As an act of rebellion, she converts to Christianity and joins the Sacred Heart Convent. When the convent tells her that only white girls can be admitted as nuns, Pauline rejects her Anishinaabe heritage and proclaims that she will only recognize her European identity. Pauline's hybrid identity is represented as emotionally and mentally destructive in the novel. In reference to Peter Barry's theory, Pauline is stuck in the "Adopt" stage.
She sees her own people as diseased or sick and in need of European succor:

I saw the people I had wrapped, the influenza and consumption dead whose hands I had folded. They traveled, lame and bent, with chests darkened from the blood they coughed out of their lungs, filing forward and gathering, taking a different road. A new road. I saw them dragging one another in slings and litters. I saw their unborn children hanging limp or strapped to their backs, or pushed along in front hoping to get the best place when the great shining doors, beaten of air and gold, swung open on soundless oiled fretwork to admit them all.

In the end, unable to reconcile her conflicting duality, Pauline is driven to madness. She is powerless against her dueling inclinations; despite her fervor for Christian purity, she is drawn to evil. She is a "windigo," an Ojibwe term for one who has been drawn into satanic madness. Pauline uses her supernatural powers to kill Mary Pepewas, thinking that she is doing the sick girl a favor. So, in the novel, disease highlights the dueling identity within the Ojibwe psyche and demonstrates its destructive power.
Sources:
Beginning Theory: An Introduction to Literary and Cultural Theory by Peter Barry.
Tracks on a Page: Louise Erdrich, Her Life and Works by Frances Washburn
https://docs.rwu.edu/cgi/viewcontent.cgi?referer=&httpsredir=1&article=1055&context=rr

https://www.academia.edu/3853780/Reimagining_the_Frontier_in_Louise_Erdrich_s_Tracks