What Causes Fever Along With Excessive Sweating?

Hi - I have a 17 year old female who has flu like symptoms. Fever (max 100.6) for past 4 days. Prior to that she felt a bit lousy. She has some enlarged lymph nodes. Eating ok, sleeping a lot, fever breaks making her sweat daily. No respiratory symptoms. I d say moderate flu like symptoms. She is on a peanut desensitization program, just started. It s sublingual small doses of peanut extract. She is also taking Clartin (but did NOT take it today), asthmanex and cranberry supplement. Also taking 400 mg advil 2-3 times a day . She has asthma and food allergies. She was an atopic baby - had dermatographism. About an hour ago she was bundled in a blanket on the couch, she got sweaty and looked at her body - the torso and arms and legs down to joints had a huge red, warm slightly raised rash. Not very itchy, not pustular, it did NOT look like hives, we know what those look like in her. She took a shower, cooled down and rash subsiding. No other symptoms with the rash. She seems fine otherwise. I gave her 25mg benadryl. Can this just be a symptom of the viral infection and sweaty overheating while rapped up in blankets? I took some pictures I can send them. thanks for any thoughts... Sharon