The author chooses to use the North Korean version of certain words in order to show their identity, and the impact that North Korean culture and the North Korean situation had on her.
When analyzing the use of these terms, the purpose of the author should be kept in mind. The purpose is to inform the reader of horrible situations that were occurring in North Korea, and to create awareness about those situations.
Using these North Korean version of words steps away from the objective, third-person view and helps the reader "understand" North Korean culture and their style of living more.
As for the term you provided (inminban), it is a "neighborhood watch system" in where people "watch over" each other and ensure that no one is doing anything wrong. This is alike to the 1984 situation of Big Brother.
