After you've talked with Anita about leaving the door open, there's a new menu item when you're in your room (Lock/Unlock Door). Just unlock the door, then go to sleep early a few times, and eventually you'll get an event where Anita sneaks in.
Make sure you've downloaded the latest publically available version from the creators
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page (v. 0.36c). I saw you were also having a problem with Samantha assigning therapy sessions that you couldn't complete.
For some reason, the version linked at the top of this thread hasn't been updated from v 0.36a, and that therapy thing is a bug in that version. There are also some other nice updates and therapy scenes for the other girls, that you can peek in on.