HANNA already knew what to do as soon as Lewis fetched her from her current room in Blanco Palace before she moved to Luna Palace.
Even though Blanco Palace was a little far from Yule Palace (the emperor's residence), she still felt the enormous power coming from something that definitely didn't belong to a human. Thus, she connected the dots and came up with the conclusion that Neoma's Soul Beast, the one that was currently inside a dragon egg, was about to come out.
And she knew what she needed to do.
[Neoma probably knows I can do it now, so she asked Lewis to fetch me.]
"Lewis, let's stop here," Hanna said, then she stopped running when they reached the entrance of the garden. "And stay close to me."
Lewis told her earlier that Sir Geoffrey Kinsley had already evacuated the servants of the Yule Palace, so she didn't have to worry about innocent people getting hurt. Still, hiding Neoma's red dragon from other people's eyes was her job.