She's clearly talking like Ikamusume, but do we tag for it, since it's not a visual parody ...?

Is it a voice actress joke? 'Cause if so it'd go under "Seiyuu connection" and whatever the name of the actress is.

Why would Nonna get the joke?

She didn't. She's just repeating what Katyusha said.

You know what , Rie Tanaka is seiyuu for both Maho and Chizuru ( Ika Musume ) ,Kanemoto Hisako is seiyuu for Katyusha and Ika , and Ika is scared of Chizuru like Katyusha is scared of Maho XD