After earning the Steward's Trust, Scarlett should visit the palace guard captain, Lucio, in the Guard Room (1) again. Ask him for work. He will send her to help one of the Palace Courtiers with a delicate problem in his apartment.
The Courtier is Antonin, and his apartment is on the upper level of the palace, at the southern end of the west wing (2). One of Lucio's guardsmen (a Marauder) is standing guard outside the door. (If Scarlett attempted to enter the room earlier, before receiving the quest, the guard would have blocked her way.) Tell the guard Lucio sent her and he will let her pass. (Click on the map to enlarge it.)
Inside the chamber, Scarlett will find a very disturbed Antonin along with two young ladies who look familiar: Venus and Vanity from the Ambrosial Lotus in the Arsenal District. Apparently, they make house calls (or palace calls.) Antonin's problem is the body of a dead Necromancer, which he needs to dispose of on the QT. His plan is to disguise the body as a servant; apparently dead servants are unremarkable.
Scarlett should leave the apartment, go down the nearest stairs, and visit the Laundry, which is almost directly below Antonin's apartment. From the table at the far side, she should grab some servants clothing; in fact, take two, she will soon need the extra. Take these back up to Antonin's apartment.