I think she’s making this too complex. We know what genre is when we see it. As she herself mentions, when you pick up the mail and see a letter from a friend, you respond differently than you do to an advertising flyer. She says we respond to much more than the textual features and formal conventions of these items of mail, but… what are we responding to besides these things? (I mean, also graphics, paper quality, the way the paper is folded, font, etc, I suppose.) But most importantly: why is pinning down a definition of “genre” important? Or does she have another project here that I am missing?
She does mention something that I think is important: she says that, though the assignment is a letter to the editor, “if you begin with an inverted triangle” (???) the audience is really the professor. I think she refers to a description of the rhetorical situation here. However, this makes me think about the idea that if you ASSIGN a letter to the editor, the assignment is really a paper for class. How do we make the genre NOT a college essay when the assessment procedure is a letter grade given by an English professor? It’s hard to shake.