Ah, no. The item is in the MC's bedroom right above one of the 2 plants inside the room.
Ok, I just checked the code.
Apparently, the item only appears when
- Iris is currently cleaning your room,
- at relationship 5,
- and you also already found the kitchen item for her Halloween event at some point.
I had forgotten that I made it this specific, sorry ^^'
I'll remove at least the halloween item requirement in an upcoming patch, since it doesn't make much sense.