Ugh it seems my Ekkie may have eaten some of a choc chip cookie today.

My 5 year old nephew came in and without my knowledge set it on the bed where she was. He swears she didn't touch it, but he's 5. I've given her lots of good food to eat hoping it will push things through. Gave her lots of water/apple in the hopes the water with help clear her out. It's been a few hours and she seem alright, what else should I do and what signs can I look for that she's getting sick??
BTW my nephew is normally extremely good with asking before he gives her anything. Had I known he hadthe cookie he wouldn't have been allowed in the room.