[Elsa does make a small noise of surprise as she's suddenly hugged and whips her head around to glance over her shoulder, but she doesn't seem too startled.]

Anna! Geez, when did you become so sneaky?

[Elsa laughs a little. Honestly, she was so focused on the new addition to their little group that she probably wouldn't have noticed Anna approach even if her sister had been stomping around.]

She's a girl, actually! According to the Pokedex. But yes, I am. [She turns her gaze back towards the Lapras, resuming the gentle petting.] I've never been this close to a baby animal of any kind before.