Dresser Hag Side Quest - Persona 2: Innocent Sin Guides
The Dresser Hag is a Side Quest that begins by speaking with the boy inside Kounan PD 3 times. You will have to leave the building and return each time you talk with the boy otherwise he will keep repeating the same dialogue over and over. On the 3rd trip he will give you the rumor involving the Dresser Hag.
As far as I am aware this Side Quest is available until Kounan PD is destroyed shortly after unlocking it during the main story of this game. Once you get the rumor from the boy inside the Police Station you'll want to go to the Kuzunoha Detective Agency and spread it the same way you do every other rumor. This will make the Dresser Hag spawn inside of the Abandoned Factory.
You'll find the Dresser Hag as a random encounter inside of the first room of the Abandoned Factory. Once defeated the Dresser Hag will drop Hag's Dresser which you can return to the boy inside of the Kounan PD Police Station for a reward of Incense Card Set.