Of course, simply asking would not suffice. As the Mother Tree's agent, the Elf Emperor could definitely peek secretly. It's said that many of the scandalous histories of the imperial family members from ten thousand years ago were the work of an Elf Emperor with quite peculiar tastes.
Nine thousand years ago, the Elf Emperor at the time, who was Kureya's great-great-grandfather and quite lacking in many respects, was forced by many members of the Royal Court to make an oath before the Origin of the Mother Tree, which the Origin also acknowledged. Since then, all Elf Emperors were unable to see any places designated by the Royal Court members.
Kureya had originally thought this wouldn't have much effect, but after she ascended the throne, she found out that most of the lands near the Mother Tree in the royal city belonged to the various noble families. Aside from her own domains, she couldn't see anything in the territories of the other dukes and marquises.