I used Hartz Flea and Tick Control Drops for kittens about 3 hours ago, Just now I read reviews that people who have used this had their cats die from it. My kitten, seems to be fine as of now, she is acting normal, but how long until I will know for sure if this product has harmed her? Should I stay up to keep an eye on her throughout the night?

If you're worried about it, then use a tiny bit of dish soap and wash the treatment off. Be sure to rinse thoroughly.