Well, logically speaking there are no reason to not check all messages if you can. However, as I know that sometimes order matters in CH, I've played different combinations, including the total ignore.
By the way, again, logically speaking, Touka should return to the class after the texting with Ren. Thus girls shouldn't be able to text or, at least, make selfie if Ren text with her at first. But, I suppose, that makes this episode unreasonable complicated.