In bringing the video to my attention, reader Jennifer G. commented that "why the viewer-stand-in character is a MUCH-too-young girl with Down Syndrome is just one of the many questions this film inspires."
So I did a little digging and it turns out that there is a reason Jill looks the way she does, and that everyone in the film speaks in simple repetition. It turns out that this film, entitled All Women Have Periods, was created for the express purpose of teaching menstrual hygene to developmentally-disabled girls. And now I feel kind of like a jerk for making fun of it.
But... Jennifer G. is right, the film does still raise numerous questions. For example, why does the family have a trapezoidal bathroom? Is their universe missing the tampon particle? Why does Jill's 30ish sister Susie still live at home? Why does Susie regard the adhesive strip's peel-off backing with such contempt? According to Jill, she and her mother "were talking yesterday . . . about periods," yet today her mother explains--seemingly for the first time--what periods are, who gets them, and what to do about them. So what material did she cover yesterday? And why aren't girls with Down Syndrome allowed to know the word "vagina?"
Well, believe it or not, there exists an All Women Have Periods Study Guide. And while it does not necessarily provide guidance on the above questions, it does contain the complete screenplay, should you wish to stage a dramatic reading.