Well, we see in the anime that sometimes Rikka would fight Touka in the chuunibyou world. My question is, does this means that Touka is a chuunibyou herself, or is she just playing along with Rikka?
Touka definitely isn't a chuunibyou. It's obvious that she is really bothered by Rikka's behavior in the first season and asks Togashi to tell her to snap out of it. It is easy to tell those suffering from chunnibyou from those who are not. Touka never makes any weird statements or gets lost in her imagination.
As for all the battles that go on between Rikka and Touka, they are all just a manifestation of Rikka's own imagination. Touka probably only swings that big spoon around a bit which turns into all those fancy moves inside Rikka's head.