Hot Red Full body Rash, help!

Al

So my daughter woke up yesterday morning with this wicked rash. It’s very hard to get a good photo that shows it well enough. But it started all over her tummy and chest. It was quite warm but I thought maybe it was heat rash and just put some coconut oil on. By the afternoon it was all over her shoulders and back and she was itching. I gave her benadryl to help with the itching and to hopefully get it to clear with no luck. It seemed to still itch and by bed it spread all over her limbs. On her arms and legs it’s more spotted and less heat rash looking. The creases of her elbows are red as well. I wanted to wait and see if I could get it to clear, but it’s now waken her for the last two hours from being so itchy and it’s still very warm to the touch. She’s has no fever and just has a slight cough which she’s had for a while. I’m planning to get it looked at, but does anyone have any ideas?