The girl does as directed. Chestnuts! 

The trick is that the place where the chestnut cart goes in the evening is also the place from which it leaves in the morning. With fresh chestnuts. Look for a window or ceiling vent without a lock.

Again, the girl does as directed. 

She locates a ceiling vent with no latch. Worming her way in only takes a little squirming and a mild act of contortion. Inside, multiple trays of freshly baked candied chestnuts cool on the counter. 

Chestnuts! She eats many, and stuffs many more into her pockets. 

A successful negotiation. Not perfectly-so, but better than has been achieved since the girl entered her rebellious phase. Good enough to encourage repeating.

Take all from a whole number of trays, and put the finished trays back with the clean ones. If they are less certain of a thief, this may be possible a second time.

Oh! That makes sense! More chestnuts later! 

She does as directed. 

And with any skill, they'll be out into the night, belly full and values better-achieved.

Was this a satisfactory exchange, girl?

“Yeah. I get a friend! And also chestnuts.”

Hm. We shall see. Let us return to your sister before she grows too anxious.

There is a secret entrance to the palace so citizens of Ardholm won’t notice their insane princess coming and going. A damp little natural passage through the palace’s basalt foundations, through a black iron grate that opens at her touch, and down into the lowest holds of the structure where her hidden quarters are. 

Sister prefers that they move quietly even through these tunnels. It wouldn't do for a servant to hear something echoing up from a below which should not exist. Or a noble, for that matter. Not that they've lost many of those to noticing the girl's existence. Except those her sister wanted dead anyway. Obviously.

Leave the chestnuts in the cave and send the maid for your sister. Wouldn't want her to be worried about us.

Elanor is there, knitting contentedly away in the girl’s chair. Elanor the housekeeper. Elanor the caretaker. Elanor the one who watches and makes sure she doesn’t cause problems… 

The girl throws her sword down on the table in front of the servant, enjoys the way she jumps… “Go find sister,” the girl instructs. “Tell her I’m back. It’s done.” 

The girl flops tiredly on the cold stone floor. 

“Oh you poor dear,” Elanor flaps her hands, knitting forgotten. “You’re hurt! Do you need…” Her words dance clumsily around an Arcanist-sized hole. “Shall I send for healing?” 

No “your grace” or “highness” or anything of the sort. The girl isn’t really a princess anymore. Not since her mind fractured. 

Water and a cloth will clean it up.

“Water, cloth, needle and thread,” she instructs. “Then fuck off and find my sister.” 

“You watch your tone young lady,” Elanor snaps, and purses her lips. “How do you expect to find a nice husband with language like that?” 

The girl sticks out her tongue but does not otherwise respond. 

Elanor sighs, purses her lips again. “I will return presently.” 

Stupid woman. Never stabbed us, though. She should suffer less than the others. Perhaps a twentieth as much. Does that sound right to you?

“Stupid,” the girl says. “About right.” 

Try to explain the mission to your sister without confusing or scaring her. She doesn't need to know the details. Couple of dead guards, framed another guard. All cultists dead, no extraneous evidence. Saved a slave, didn't know anything, want some money so she leaves and doesn't talk.

“Details,” the girl agrees. “What if she wants us to kill our new friend? Remember Lord Mclear? And he was a lord, not a slave.” 

Don't say she's a friend. The elf is a loose end, but one that you're cleaning up. You're the expert on how to get rid of people, after all, and once you have a bit of money for her to get out of the city, your sister will never need to hear of her again.

“She’s my friend, and I like her.”