Is she currently on any flea medications? If you do use a flea shampoo on a dog that already has had a monthly flea treatment, it may be possible to overdose, and therefore have this reaction.
I know that this poisoning is much more common in cats, and normally caused when people apply dog flea products to cats.
If this is the case- you probably wouldn't have a leg to stand on in court.
This poisoning can also be caused by other insecticides, such as surface sprays, flea bombs, insect sprays, etc.
It would be unusual for a dog to overdose on just the flea shampoo without having been contaminated with another dose of the poison coming from somewhere else (eg. flea treatment, insect spray)
You would have to discuss whether it was the shampoo and only the shampoo that caused the problem, and then go from there.
Once you have consulted your vet, I would definately contact Hartz and complain to them about the problem- even if it did work out to be caused by an overdose of using too many pesticides- there should be warning labels on the bottles instructing that these products are not safe for cats, not safe when used in conjunction with other pesticides, etc)