Ryga's primary characterization of Rita is as "dependent and expendable" before a "dominant" culture that has historically and continually marginalized the dependent culture by ostracizing and isolating them on "reserves," as reservations are called in Canada. Ryga's secondary characterization of Rita relates to her persaonal situation and choices.
She is a marginally educated young woman with little monetary capital who chooses to go to the unnamed city (recognizable though as Vancouver) to get a job. Instead of finding what she expected, which was opportunity and work, she found herself without means to care for herself or to get back home. Now the tertiary complications of characterization begin.
On her first attempt to get back home, Rita accepts five dollars from two strange men who seem charitable but who are undercover police who have stereotyped Rita as a streetwalker, have "paid" her in an entrapment and have arrested her. Now her characterizations as a social degenerate begin, then culminate in the Magistrates denunciation of her:
The cities are open to you [Indians] to come and go as you wish, yet you gravitate to the slums and skid rows and the shanty-town fringes. You become a whore, drunkard, user of narcotics ... At best, dying of illness or malnutrition ... What is to be done? You Indians seem to be incapable of taking action to help yourselves. (Magistrate to Rita)
Her final characterization is of the ultimate marginalized and infantilized victim (one who is rendered powerless and treated as though helpless) as she is brutalized and murdered.