She's wrong, you know. And also right.

She was talking about a different book in the series, "Prisoner of Azkaban". Mad-Eye, in "Goblet of Fire" encountered the map and borrowed it from Harry for the rest of the book.

But it actually wasn't Mad Eye; it was Barty Crouch Jr. in disguise. He was taking polyjuice potion to impersonate Mad Eye all year. There was no point in the books where Harry got the map back from the imposter or anybody else, but Harry had it in his possession again the next year. How did he get it?

So you wife is both right and wrong. Do what you feel is safe with that information.

Also, Snape knew what the map actually was, if not before, then certainly after the events at the end of "Prisoner" because he found the map fully activated and showing everybody on the grounds of Hogwarts when Lupin left it "running" in his office as he ran to the Whomping Willow. Why did he not demand the map after that or at least tell Dumbledore about it? They could certainly have used it as a security measure at the school. Ther would have caught the Mad Eye Moody imposter earlier in the next book with it.