Okay, thank you for the additional information. What you gave her actually shouldn't have done what you are seeing. It takes a LOT of dewormer to cause a toxic reaction. You definitely need to get this baby some food. Also, Hartz products have been proven to have problems - especially flea products, so don't give ANY Hartz products to this particular girl again because it may be part of what is wrong. I truly don't think you overdosed her to where she is at.
Go to the store and get some Gerber Baby Meat - chicken or turkey and try to get her to eat some of that. I would leave dry food out for her all the time until you know she's eating well, and get some Pedialyte also. Use a dropper (you can get one at the drug store) and give her one dropper of pedialyte every 10 minutes for an hour. If you have to, use a feeding syringe from the pet store to syringe about 5-10 cc of baby food into her every 20 minutes for an hour - if she'll eat on her own, all the better.
I really think there is some neurological problem going on with your kitty that the vet needs to evaluate. If she is still having problems 2 days after taking the dewormer, she needs to be seen. The most important thing is getting food and liquids into her now. If she doesn't start eating, she will develop hepatitic lipadosis (fatty liver) and the only cure for that is food. We want to stop that before it starts. She probably won't be very happy with you making her eat and drink, but you really need to do so. Call your vet in the morning and if you still have the dewormer, take it with you. It may be defective, and if so, the vet can have tests run on it. At that point, you can contact Hartz and take whatever action you and your vet determine is appropriate. Just to give you an idea of how safe dewormers usually are - an 8 week old kitten should get about 1/4 of a cc of dewormer. A tech at my vet's office accidently gave a litter 1 1/4 cc of dewormer and there was no problem with any of the kittens. If it were something that could be toxic with just a mild overdose, it wouldn't be over the counter.
Please let me know how things go with your kitty.