Clean up after you're done, put all clothes back on her and blanket (remove accessories, sweater as well) don't let Kan see her naked
All of the above prevent you from gaining suspicion
To reduce suspicion simply skip a few nights, give her gifts (if you have)
To have sex you need to buy two upgrades from the peeptube shop - stabilizer (unlocks mouth) and hands free mount (unlocks dick), to buy one you need the other