Actually, I think Kanako is afraid that her image as an "Idol Goddess" would be compromised if she's seen using a public restroom.
Sanae clearly doesn't think much of Kanako's self-declared "Idol" status.
Toilet
Be it big or small, just do it!!Please! Anything is fine, as long as you can do something about this!!Yes! Please, Sanae!!That’s impossible. I don’t think my power will work on Suwako-sama…ToiletGetting Suwako-sama out of the toilet?What are you talking about!?Even without doing so, you could just use the visitor toilet outside…ToiletIf any follower saw me in such place, my position as an Idol God would be…Ido-!?Uwah!