She probably recognized that the perp was not all there and shunned his advances. Or sometimes it takes going out with someone a couple of times to realize what fruitcakes they are.
I think this was the girl that loved animals. She was probably drawn to underdog figures and saw that the perp was kind of lonely. but then realized that he was dangerous.
How sad the quality of people that this idiot slaughtered
One of her friends said on a blog tribute that she was "nice to the dorky eighth graders" indicating, that she had a good heart. She loved animals too.