I believe The Rez Sisters to be a good play for teenagers to study in High School, but I can see it's potential for being a bad play to study as well.
The Rez Sisters has great key ideas that teenagers could understand. The characters are well written, and relatable. They're kind of like someone who you'd meet on the streets of Orangeville, and perhaps that why we (being the youth of Orangeville) like them so much. The actual context of the book is a social issue that is relevant in our society, and the racism and hardship that Natives in Canada face is a topic that children in Canada are finally learning about in their curriculum. We know something about this topic, making it easy for us to discuss it in class, and fathom the main ideas of the book.
But perhaps for that very reason is why the book is not a good choice for a novel study in class. I'm not saying that we should ignore the issue, or make it seem like it's not important, it just might be a good idea to bring other social issues to light in class, especially those that everyone might not know a whole lot about. Doing this makes teenagers aware of more than one issue, and helps us have a better understanding of the sensitive issues that appear in books like The Rez Sisters, such as rape, poverty, and abuse. By doing this we can become aware of the problems in our world and society, and potentially fix these issues as we grow older.