From a political perspective, even if Astrid's initial thought was that the two princes were incompetent and she wanted to choose a new monarch, she actually had no reason to take Amalia out of the palace.
It would be much more convenient to hide the choice plan, keep a low profile, wait for the two princes to attack each other, and when the time was right, she could then, with absolute advantage, enthrone Amalia, who was easy to control and possess royal blood.
At least from Hibbort's perspective, Astrid letting Amalia leave the ancient castle too early, while allowing her to learn the ways of a monarch and study statecraft faster, the hidden dangers within far outweighed the gains.
If Alistair or Lucas had discovered Amalia' escape early on, Astrid's plan would have inevitably failed, and it would have been difficult to regroup and counterattack in adversity when everyone was on guard.
