Itsuwa made her first appearanace in Volume 11, during the trip to Italy.
Though they say that the Amakusa Catholic Girl that Touma fought in volume 7 could have been Itsuwa. (and that might have been the time when she fell in love with Touma
) It was mentioned in volume 7 that the girl's name was Urakami [浦上]. Rumors say that Itsuwa's full name might be Urakami Itsuwa 「浦上 五和」