IN THE MOVIE "A WALK TO REMEMBER" (BEST MOVIE EVER) But i have a question. please answer?

she somehow knew that if he got closer to her he would fall in love with her. and she was going to die soon anyway and didnt want to leave his heart broken. i love this movie eventhough it is soo much more different than the book. they made such a cute couple.. it was soo sad whenever he would cry.