You have to buy the extra-strength sleeping pills off the internet and spike her drink when she's doing yoga in the morning. You then get to have your way with her while she's KO'd. At the end, you pop on her face: If you want to repeat that action, clean her off; if you want to progress the rape chain you'll leave her face decorated. Leave the apartment and she'll immediately call you and say you're horrible and that she's changing the locks. Then go online and buy the special key making tool, then see Brick at night and get a mask. The next day, go to the Park around 1300 and see Nina jogging. Follow the prompts, and you force yourself on her in the Park. After this, her apartment is again open to you. Eventually, you can tell Shura about her, and the two can go all Chinese finger cuffs on her.
EDIT: per Laserdisc Johnson's note, the extra strength knock out sleeping pills are obtained from the doctor in Chkalovsky.