@Wolfwhistler Haha, no, she appeared in the middle of Kumo's argument with herself. She even had time to deny the possibility two times. It was a discussion already. When you hear an urgent warning from a reputable source (if you don't count yourself as a reputable source, it's time to visit a shrink), you react immediately, without asking for further descriptions and especially without trying to present counter-arguments.
Consider this in the military:
Warning: "It's a grenade, get down!"
You: "No, I don't think they have any grenades left."
W: "What? I just saw them launch it!"
Y: "Still, how likely is it that they would have any left?"
Grenade: "Boom. You are dead. Congrats."