You have to trigger 8
different Suspicious events, as far as I can tell, and then see one of the two triggering Peeping events to see her for real, in other words she needs to be banging both of the dudes.
Suspicious Events:
- Warehouse Noise
- Library Behaviour
- Bathroom (when she's not alone)
- Toilet (Dude comes out, check she's still in there)
- Kitchen event (triggerable if you walk in dining room and her pic is wearing naked apron)
- Tokishi in his room and kicks you out
- Girl's room - she blocks you from checking the wardrobe
- Dressing Room - changing clothes event.
When you see all these, the two triggering events become available; either behind the warehouse (through the Safe room), or the panel at the back of the leftmost Japanese room.