I just watched the footage of the incident, and this is what I see: Budd was in the middle of lane one and Slaney was inside her on the rail coming off the turn, with Budd ahead of Slaney by a body length, but the back-kick of Budd's stride looks like it would overlap with Slaney's legs if Budd were to veer to the rail.
As they proceeded down the straight, it looked like they held the same relative positions when Budd tried to veer to the rail, and got tripped slightly as her back kick caught Slaney's foot. Budd regained her balance and veered back to the right slightly(the middle of lane one again), but a few strides later, she tried to veer to the rail again. Unfortunately, Slaney had held her ground on the rail, and this time, it was Slaney who got tripped, and the rest is history.
It does not look like Budd made any attempt to accelerate as she moved to the rail either the first or the second time, nor does it look like Slaney either accelerated or decelerated during the entire chain of events.
This is the way I see it. Is there another way that you would interpret this? Who would be at fault if this interpretation were accurate?