I should caution here: I agree with your reading interpretation! Wilder totally made it seem sad/unfair/mean of the government that they had to leave Indian Territory (almost hilarious in retrospect that she's upset they left, but the name she uses for the land gives ownership to a different group of people).

I don't deny her rosy-pictured sympathetic-to-white-pioneers view....the only point I was trying to make was that when I finished reading the book, it was clear to me that they had built their house on Reservation land, and that was why they had to leave.