Last time I did something similar it was exam period. It went like this. I met her to borrow a book from her to study and we started talking...
-bla bla bla... God I'm so fed up with studying. I think I need a little break.
(... bla bla bla)
-It would be nice to drink something and just let loose a bit.
(... bla bla bla)
-You should come over next week. We'll watch a movie and drink something.(very obvious. No girl is that stupid to not get this hint. But it looked like she seduced me into doing this. Girls love that shit

)
She agreed and after we finished our bottle of vodka we were banging for 4 hours straight. My neighbours in the dorm were not happy and I had to wear a scarf on the exam that was a week later(!!) to cover up the hickeys lol. Girl was a real beast.
Before she came over we talked a few times on fb and I was quite sexual and making sure she knows what's going to happen(and is looking forward to it)
So that's the key I think. Be smooth, but bold at the same time. She either wants the D, or not, but this is the single most efficient way of finding it out.