Solution

On the left path, solve the ore puzzle (Green NE rubble & Yellow SE corner), then open the door in the secret area immediately after Nanamo finishes talking.

Description

What a surprise to learn that the old palace silkie was a creation of Mother's! The discovery impelled me to pursue the topic with Papashan, who, of anyone besides Father, knew my mother best of all. Naturally, I was circumspect in my inquiries, lest he become aware of my subterranean explorations.

With fond remembrance, Papashan spoke of Mother's penchant for cleaning─a habit she refused to surrender even after taking up residence in the royal chambers. Her ladies-in-waiting were positively scandalized, and hid away every brush and broom that the sultana's hands not be sullied by common grime. Denied the usual tools of sanitation, Mother retaliated by employing a Sharlayan tutor, whereby she acquired the arts necessary to manifest a massive, mouselike familiar. Ingrained with an obsessive dislike of dirt, this arcane entity would even corner the palace guards to scrub spots from their armor─to the great amusement of the household staff. Then one day, without fanfare, the silkie was simply gone.

I suspect the cause of its disappearance lay in the deepening conflict with the Monetarists; with less and less time to slip away from the palace, Mother likely set her familiar to protect and maintain the secret garden in her absence. Yet what a stubborn and willful soul she was! To create a servant for cleaning is one thing, but to imbue it with such unbridled power is quite another!