Serini has the same problem Redcloak does: she is invested in her plans for emotional reasons and is unwilling to change her plans when presented with evidence that workable or even superior alternatives exist.

Redcloak feels that if he changes his plans now he will lose his justification for past atrocities he has committed, and he's willing to commit new atrocities, like trying to murder someone who offers alternatives, in order to keep them.

Serini is deathly afraid of Xykon and feels she is inferior to the other gatekeepers whom he defeated, and so she is desperately trying to avoid another direct confrontation with Xykon, to the point of being willing to let him win.

V had this problem too. So did Tarquan, Nale, and Miko, for that matter. It seems to be kind of a theme in the comic.