Spoiler Alert - Click to ToggleIt just didn't seem plausible, and also the fact that Leo chose not to tell her that one thing when he was trying to tell her everything else. I guess it falls into the same trap that a lot of movies fall into: It would just take the lead character sharing one fact with the other character, and the movie would be over....but since there's still 70 minutes to go, the critical fact must remain shrouded in mystery for a while.
Spoiler Alert - Click to ToggleSo all this does is give you the impression that she's not really this wonderful person, she's just a tart who is easy to coax into bed on the first date.