Her head leans back as she sees the umbrella being put over her head. Now that the rain wasn't pelting down on her head, the water that her hair had soaked up dripped from the ends and down little rivets on her childish features.

"Nuh-uh! I won't get sick! The rain is nice!" When Yotsuba looks down, she sees that they're at a random puddle ... and she jumps up to splash in said puddle because that's what she does.