Suggest Treatment For Accidental Consumption Of Full Bottle Of Tylenol

My 13 month old daughter (23 lbs) managed to get a hold of a bottle of Tylenol PM (generic brand) (500mg). She had it open, with one pill in hand, and a few on the floor. There weren't many left in the bottle, although I'm not sure how many. We didn't hear her cough or choke, and she had nothing in her mouth. Due to the fact that I am not certain how many were left, I am also not certain if she swallowed any. She is acting fine and normal; this happened almost two hours ago. What should I do? And is there any way to look out for signs of possible liver damage? Thank you.