I mean, I'm pretty sure that's precisely what she thought it was. According to other news reports, she actually cleaned it in her hotel room so her suitcase wouldn't get dirty.Y'all hating right away but look at it all rusty and shit. It's old as hell and a lot of people might just see it as a historical souvenir and not dangerous. Also she declared it. This isn't as dumb as people are making it out to be.
But that begs the question, what did she think it was? The shape should be enough of a hint.