Taiga appears as the homeroom teacher of Hakuno Kishinami, Shinji Matou, and Leonardo B. Harwey during the preliminary round. She is programed to trip in exactly the same way each day during the prelims, and thus the one day she does not, the potential Masters notice that things are more obviously wrong. Rumors during the prelims state she's living with a student, which she denies, stating he is a friend of the family and she only visits to help out, an obvious reference to Shirou.
During the Holy Grail War itself, Taiga aids Hakuno by providing quests to complete similar to those in traditional RPG games. Her rewards range from items to furniture which Hakuno can use to decorate his/her private room with. Completing all of these quests will cause Shiki Ryougi to appear in the game's bonus dungeon on a new game plus.
During the prologue, Taiga does not appear as Kiara Sesshouin has hacked into her profile and replaced her, similar to how Julius B. Harwey replaced the Souichirou Kuzuki NPC. In the Far Side, Taiga appears again and provides quests to Hakuno as in the previous game.