In the GN, Lori's between a rock and a hard place, and she knows it. In the movie, she's been so completely manipulated that she only barely gets away from Jon. She's a demi-bitch at most in the GN. I found her human but forceful in a way that you would expect from a hero.
In the movie, she's never abrasive. She's always trying to please, and she goes from Jon, who cares about her but doesn't see the point in investing any energy into it, to Dan, who's attracted to her and badly needs a friend. So, from uncare to desperate clinginess.
And yes, I mean that she's acting in a way that will excite a man, but is insincere. It's only in contrast with Dan's expression that I saw that, by the way; if it was a really porny scene, if Dan didn't have a beer belly (that mysteriously vanished when he put on his costume, oddly), if he didn't have his awkward glasses, if his face wasn't strained and undignified while they were fucking, it would be different. But her perfect O face and gasping sounds were a sharp contrast. That's not to say that she didn't go to his house for perfectly human reasons, that she doesn't need love and attention for perfectly human reasons. It's just that her needs have been put to the use of the Army for so long that her "training" the only way she knows how to fulfill them.