Are you sure your wife was telling the truth? At its simplest, pastry is basically a combination of flour and fat. In pastry, the fat performs at least two functions: it tenderizes by keeping flour proteins from joining to form gluten, and creates flakiness by keeping space between thin layers of dough (of course, butter also adds flavor, while vegetable shortening does not). Without the fat, what you have is a cracker or flatbread. A nonfat yogurt would add moisture and flavor to your cracker or flatbread, but it still would not be pastry.
We’ve checked no-fat cookbooks, low-fat cookbooks, yogurt cookbooks, and baking books, and have not turned up a single no-fat pastry recipe. Sorry, if you find something, please let us know.