You'll first want to determine if your rabbitactually has a fever. You can take the rabbits temperatureyourself, or a vet visit may be in order. Sometimes arabbit's ears may only appear to be hot if they have been runningaround or holding their ears over their back. The fact thatyou mentioned the rabbit is also not acting herselfmaybecause for concern.
Here's a post I made in Nov.:
Now that viral season is upon us with a vengence, it's important toknow how to take your rabbit's body temperaturebecause a riseor fall in body temperature is often the first sign ofillness.
"All pet owners should have a baby thermometer. Apply some lubricant tothe thermometer, insert it gently into the rectum, and hold it therefor about 1 minute. Normal rabbit temperature is about 101o F to 103oF."