How to help my cat after spaying?!?

Okay i picked up my 11 mnth old cat from the vet this afternoon after being sayed and she was tired but she slept for a few hours on and off when we got home...a little later she started vomiting white foam, just the white foam, no food because she hasnt eaten (i know it is normal for her not to eat OR drink after just arriving home.. i also gave her small amounts of water in a syringe just so she doesnt become dehydrated and she swallowed them just fine.) She was of course given a pain reliever before leaving the vet ( i dont know what ) and the vet said it would wear off soon. They asked me if i wanted to purchase additional pain reliever fr at home BUT i wasnt aware it was going to cost me and i didnt have the money right now. its now very late at night and she has been just laying down i want to know what i can give her for pain because im guessing what she was given at the vet probably wore off by now but im not sure because i know cats can hide their pain very well.... IS IT OKAY TO GIVE HER CHILDRENS LIQUID TYLENOL wih a liquids syringe ( i have in my medicine cabinet ...The RED liquid childrens tylenol and a normal not childrens one which is BLUE) I have not given her any yet! i wanna know for sure if i can but from my research ive seen yes NO yes NO yes NO! so i have no clue?!!! please help me.... NO STUPID ANSWERS PLEASE!! thank u in advance!