Leticia used "Blunt Honesty."
It's Super Effective!
And it's the one thing about the vast majority of isekai stories out there that boggles my mind: Why in a world literally overflowing with magic, monsters, and incredible things beyond our own Earth's fantasies as the reality of every day life would the very simple (by comparison) idea of "I came from somewhere beyond the world we're living on" seem like it's too far fetched to broach?