Fevers can also be caused by extreme stress or anxiety. It could be natural. Never rule that out. If her temperature is taken and is over 101F then she should take some ibprophen. Over 104F and she should be taking a trip to the hospital.
You really have to becareful with using fire in a body however.
In case you used fire in her body, I have to ask, did you remove the energy you put into her? The energy served it's purpose and should have been drawn back out. If not, she could be sensitive to it. Check with a thermometer. If she feels hot but does not actually have a heightened temperature, then she is sensitive and you need to finish what you started. I use stones to draw out additional energy. Too much energy can make you feel very hot.
By lower entity, what exactly do you mean? You're not very specific on exactly what happened. I'm not sure if you used energy on her or the house. And what this "entity" is.