When Elsa is playing with and chasing the elephant herd, she is not wearing her collar. But in the next scene when she returns with an elephant calf, she is wearing her collar.
Before George has told Joy that he still has Elsa while they are driving back, it can be seen that he isn't situated directly behind the steering wheel but rather a little to the left of it. This may explain why the truck is shown to be swerving.