When to take 1 year old to hospital for fever?

My 17 month old has a fever of 100.3. Shes eating and drinking fine and has had a wet diaper since she woke which was only 3 hours ago. When i checked her temp at 1pm when she woke it was 99.4 and i gave her food and a lukewarm bath and we just came down and its 100.3 so i gave her some tylenol since whenever she gets a fever it usually spikes pretty quick. She physically is acting fine and talking and listening to music and eating fine and eating a popsicle now. But what temp would i need to take her to the ER? Just in case.