I'm pretty sure that the keys reference were to drugs, and could be either marijuana or cocaine (rock). If the two keys in the photo referred to 2 kilos, which is a large amount, it would appear to me that it could be split among more than one of the people at the apartment, or possibly EA (or someone else) was doing some dealing on the side. If this is correct, then Christina had both her car keys and her house keys that night, and all the keys references were drug related
I'm not sure if this has been posted before, but see examples below.
http://www.urbandictionary.com/define.php?term=Kilo+(or+Key)
Trying to interpret the text Christina sent HF asking him to leave the door open because she has lost her house keys. I don't know if "lost" means a possible lost sale, or if "leave the door open" means he should be open to making a sale. I don't have a clue what that means.
But this has me convinced that Christina's disappearance has more to do with drugs than a sexual motive. It's possible one turned into another, but drugs seem to have played a big part.