Though X is admittedly not the second strongest of the Niisens, she has the most mystical power in comparison with all the others. Her powers are kind of like the other subset from Joubutsu's, after all:
Joubutsu exists to see through the death of every being in the worlds
X sees the fate of the people while they are still living.
While X is under her insane mind, she actually breaks her own rule of "don't bend fate" by letting the fate of anyone who consults her be twisted by X herself. Since Saitama is already with them by the time they approach her, she barely pushes Ryougen out of the way and potentially alters his future for the dull.
I'm still in the dark however as to how they'll actually fight X, though.