"She's inconvenient to transport, I don't really want to kill her, she's dangerous to leave anywhere. I wish my friend were around. It's pretty unlikely that he turned up in the past day though."
"I don't really want to kill her either. But I don't want to let her go. Could you, I dunno, keep her for a while? Until your friend shows up? When is your friend gonna show up?"
"I can't keep her under control if she can't be vassalized, so she might hurt me or my tree or something, and it could be years before he visits again."
"I don't want to kill her if I don't have to." Promise taps her foot. "If I knew exactly where the gate was, I could put one directly in front of it that led somewhere else in the mortal world, someplace she wouldn't want to go, and then she couldn't get into Fairyland, it would just be in one gate and out the other. You were there a while, can you think of somewhere good?"
"I didn't really go out of the house... you could put it to an ocean or something. There's oceans. Or you could put it to right back where she started, for that matter."
"Yeah, that works. And when my friend comes by he can close them both. Will you show me?"
Promise goes through the gate and back a few times, figuring out exactly where it is.
"I'll make it facing the opposite way so we can still put her where she came from after it's settled," Promise explains, and then she starts the new gate. "But this might take a while."
"Do you mind staying and taking shifts watching her? I'll keep her stuck in the ground and inaudible, but if Nap or somebody comes for her..."
"...And after that would you mind if I commanded you not to lie to me so I can check your secret and then maybe told you my name?"
"Depends," she says. "Are you gonna keep me and take over Fairyland and make everybody call you Princess?"
Especially not the Princess part.
"I mean, there are things I would like to do that you would be very useful for but I'm pretty sure I could accomplish most of them by telling you my name and then occasionally sending you mail."
"But not in front of the Princess, because if there's anything wrong with your information, if you forgot something or don't know everything about how it interacts with mortals, it would be bad."
Promise makes sure that the Princess is securely fastened, thoroughly inaudible, and not about to die of anything. And then she curls up on the ground and goes to sleep and mutters words. (None of them form enforceable, let alone enforced, commands.)
The princess sobs and picks at the earth gripping her feet and mouths words. Eventually she sleeps.