I don't remember Iris seeing them together at this time in the novel. If I'm not mistaken, it was Mirelle who followed Aria and Iris gets to know about them just a lot after in the plot. I should probably re-read (a story about such cunning and actually really villainous heroine is always nice to read again) since my memory sucks. Lol
But even if it's different from the novel, it's very nice seeing Iris so distressed. Burn witch with b! Burn!
Edit: Had to go back and read this chapter (in the novel) again. She really saw it all! Lol
Love it! Like when you forget to take money out of your pocket and some time later "find" it, lovely surprise.