What kind of thermometer did you use?
On the instructions, it will say what the temperature reading means.
Meaning, rectal temp, underarm temp, forehead temp... which all varies.
Rectal temp is most accurate.
Forehead or arm-pit temp, is usually 2-3 degrees less, than what it actually is.
Don't give her anything orally, without talking to the Doctor. As an FYI, things like Tylenol only masks the fever, or brings down the temperature... NOT curing the illness. So the fever may come back.
Also observe her.... and keep up nursing or Formula if you are doing that. So she does not get dehydrated.
Call your Pediatrician... and ask them, but a Doc will not "diagnose" over the phone. They have to see the baby.... because a fever could be due to many reasons.
All the best,