Yes, but didn't Ariake no Kata complained about the additional heat from the water mirror?
Anyway, I REALLY doubt Kasumi is saying the truth at the end of the episode. She's definitely lying again, someone like her won't be scared of beach of all things, especially since just a few episodes ago, during Surfermaru's debut, at least half of the episode is on a beach, and she doesn't show any signs of fear. In fact, one scene involves everyone walking towards the water!
Though to be fair, would you really say your actual fear in front of everyone, especially after knowing at least one person in front of you is willing to prank you out? I think it's natural for her to lie again.
Personally I think her real fear is being sent back to the stone age or ice age, before the advent of any modern technology.