Revealing mistake: Loder gets scared and tries to get away from Kara. He takes off down the road at a significant rate of speed. Kara uses her super speed to get in front of the car. Loder has to slam on his brakes to keep from hitting her. At the speed Loder was going at he should have either skidded to a stop or hit Kara with his car. Loder is able to stop his car without doing either.
Plot hole: When Kara realizes that Agent Loder is listening in on the conversation, she runs out to his car to stop him. She has Clark's ability of super speed which she uses to get over to Loder's car. As she runs she ends up running through a wooden fence and you can see, through the motion blur of her movement, she neither jumps over the fence or goes around it yet the fence never gets damaged from her running through it.