make sure you've already found and done the part with Marin during Rinny's quest otherwise you'll need to cheat it in like Indivi said, after you're done with all of Rinny's stuff at the mansion, go to 2nd floor and to the right and find Marin and continually ask for acceptance, then follow what she says until you're giving her a massage, then grab her clothes to easily get the quest done. after that, leave (or sleep) and return to her, you can buy the clothes off her for 1200 (Also make sure "Female Partners" is enabled in kinks or you won't get to do this)