
Dogs heads are much tougher than ours. When my last dog got hit by a car, he took the brunt of the force on his head
(it knocked a couple of teeth out and turned both of his eyes blood red from the bleeding in them), the moment we jacked the car up & untangled him from the axle he shook himslef down & wagged hiss tail

He had many flesh wounds, but his head was fine with nothing to worry about afterwards regarding his head.
I don't actually know what the signs of concusion would be for a dog, but I suppose difficulty being woken from sleep, apparent visual/mobility problems, confusion and basically anything out of the ordinary would be an indication that at the very least a vet-check is in order.
I would be more worried about a neck injury from the force of hitting the fence and would be keeping a very close eye out for any indication of that.
Best of luck for your girl, gosh they worry us don't they!