Either way, she cut the rope swing to cover up her crime and make it look like an accident. She could have killed Leslie in some other location (who knows, she may have even broke into Leslie's house and killed her there) and then brought her to the riverine. In fact, it possible that Miss Edmunds didn't even kill Leslie at the riverine. Miss Edmunds either pushed Leslie from the log and actively prevented her from getting back onto the shore, or bludgeoned her and then tossed her into the river to drown.

This would have given her the perfect opportunity to strike, and the river rising as a result of the storm, would have given her the perfect way to hide her crime. Miss Edmunds was in the area and noticed Leslie was alone. I believe that on the day of her death, Leslie had went down to Terabithia before Jesse had woken up (she was already dead by the time he and Miss Edmunds passed by her house). I believe that Miss Edmunds had been stalking Jesse and Leslie for quite some time and eventually discovered the location of Terabithia. Also, Leslie displayed a dislike of Miss Edmunds, maybe she was suspicious of her very unprofessional behaviour towards Jesse (Leslie is shown to be very intelligent for her age). Miss Edmunds clearly wanted Jesse all to herself, but Leslie's strong friendship with Jesse was a massive barrier to her grooming of him. The only thing standing in the way of this was Leslie. His childish crush on her just made it all the more easier for her to groom him. A pedophile like Miss Edmunds would have quickly picked up on this and begin preying upon him. Jesse is isolated both at home and at school, he feels neglected by his parents (especially by his father), is bullied and doesn't have many friends at school barring Leslie. I theorise that she is a dangerous pedophile who has eyes for Jesse. I strongly believe that Leslie's death was the result of foul play, and who do I believe is the culprit?. I reckon that the rope snapping justification was actually a nefarious way of covering up the crime. Even though she is a child, she would have had the sense that using the tree rather than the rope, was a far safer option. It is far more likely that Leslie would have used the fallen tree to get over the riverine, rather than the rope, especially with the river being higher and running faster than usual. It is revealed in the film that a large tree had been blown over the ravine by the storm, and formed a makeshift bridge across it. I don't believe the whole 'the rope snapped and Leslie hit her head and drowned in the river' theory. I propose that Leslie's death wasn't accidental at all, not even close. (PS this theory only applies to the 2007 movie)

The bridge to terabithia novel