It used to take a temperature of 102 to cause a rash, but most recently all it takes is a temperature of 100. In addition, the last 2 times I had a fever, the fading rash turned itchy and the itchiness lasted 4-5 days. Anti-histamines helped the itchiness somewhat. I'd keep using the antihistamines. She is a cocaine user, and I have heard from people of a fever called Cotton Fever.
Drug users get all sorts of different fevers.
You are correct to be worried. Tell her your concerns and be available to help. However, don't be surprised if she doesn't pick up on the offer. Along with this I have had extreme swelling and soreness of the inguinal lymph nodes. Blood tests show no infection.