Borders

The article "Borders", written by  Thomas King, demonstrates a story about a "blackfoot" mother never admits she is American or Canadian when she pass the national border. The main border in this article is not the physical national border. As far as i concerned, it is the border between the aborigines(blackfoot) and non-aborigines( Canadian or American citizenship). Also, I think there is a border between what "mother"  believed and are proud of in her mind, and what others want she to be in the real world. When stay in the national dividing border, "Mother" always admit she is "blackfoot" and never said she is from Canada or America. Obviously, "mother" is proud of her identity of "blankfoot",However, the border guards want her to tell the true citizenship and don't approve her identity as a blackfoot. In page 135 and 136, the border guard just asks mother the same questions several time. Though the guards are just do their jobs, we can see that the identity of blackfoot does not work when you want to pass the national border in the old years. Mother's abiding beliefs are not same as the real life she has. 

Questions: Telling the border guard the true national citizenship is the wise way to pass the national border. Why mother does't want to admit her citizenship? Why she insists that?