It could also be that Joran struck up a conversation with Stephany because he saw she was winning. His plan was to steal the money after he got her into the room, and figured she would not realize it until he had skipped out. So he slipped something into a drink she already had or that he bought for her. (There has been much talk of him being broke.) He probably did this right before the casino closed so that the drug would be just taking effect as they left. He charmed her, pretended to be a gentleman by walking her to her car. By then she was feeling woozy, and maybe even thought she was getting sick, or had eaten something that didn't sit right, etc. So this "gentleman" (as he was pretending) suggested that she should not drive in that condition, but that it would be fine with him if she went back to his room with him, just to sleep it off. To gain her confidence he didn't make any advances to her at all en route to the hotel. A sexual assault was not his first motive, although that would have been a nice addition to his night, no doubt he would have thought.
At any rate, they get to the room, she by now is ready to sleep. Maybe he planned to take the money in the morning so that she would not have time to notice it was missing. But, when morning comes and he starts to execute his plan she awakens, sees what he is doing, and confronts him. That is when he went into a rage, and Stephany lost her life. Just pure conjecture here, but seems plausible to me. JMHO