Valby did not run the tangents or keep to the inside of curves very well. If she was following the cart she sometimes seemed to follow the camera cart not the lead vehicle cart. The camera cart frequently was wide on turns to get a better filming angle of her. Had she run tangents and turns better she still may not have won, it may have been closer or who knows...
I do not believe Touhy planned, wanted or 'measured it' to allow Valby to run out to a 10 second lead where she was out of sight on some turns and then depend on closing that gap at the end. Finally catching her with about 500 to go is cutting it close. If your goal is to win you do not want to spot your main competition a 10 second lead, unless that runner was just going ridiculously too fast.
Obviously Touhy was much stronger and faster than Valby at the end, but has anyone been able to determine (based on relative splits from other runners) if Valby died at the end, Touhy really picked up the pace, or some combination of both?