I have to wonder if this is her Scottish teacher's influence, because if my reading British literature/watching British miniseries has taught me anything, it's that they enjoy their plain toasted bread over there.
On the other hand, for my entire life, "toast" has always meant "toasted bread + butter and cinnamon sugar," and apparently I've passed that idea on to my children. Hence Miriam's surprise at plain toasted bread being called "toast." If I wanted (for some unfathomable reason) toast without the butter and cinnamon sugar, I would have to say, "dry toast" or "plain toast" or, you know, "toast without butter and cinnamon sugar."
How about you? Is the idea of toast = toasted bread + butter and cinnamon sugar an American construct or just a Bridget (Walker family) construct? If someone offered you toast, would you feel compelled to ask if they wanted butter and cinnamon sugar, or is that included in the concept of "toast"?