I think whenever Toki called Ricchi, in the next turn she will get the tile she needed to win. This meant that someone has to change the drawing order in order to prevent the ability.
For example Toki called ricchi and is tenpai for 2 circles. From what I can get from her ability this meant that the 2 circles is set to be drawn by Toki in her next turn. For the purpose of this discussion, the wall has the tile 5 circle, 3 circle, 1 bamboo and 2 circles in drawing order. If no one changes the drawing order( call a pon or kan), player 1-3 will draw the 5 circle, 3 circle and 1 bamboo leaving the 2 circles to be drawn by Toki when her turn comes.
To prevent this a player could do a pon or kan which meant that a player will not draw from the dead wall changing the drawing order. For example, the next player after Toki discards 8 circles, if someone pon or kan the 8 circles. Then that player would not draw from the wall. This meant Toki will draw the 1 bamboo instead of the 2 circles needed to complete her hand. The 2 circles that Toki should have drawn will then go to the player after Toki's turn preventing her from winning.
Its a nifty ability actually, but I don't think it will work on Saki who can decide to Kan and get an extra draw which will be mess the drawing order. Or anyone who has some supernatural sixth sense. Even someone without a great ability can stop it, though it would need two players. One who will deal a risky discard and one who can pon and kan it.