You say she works outside. Was she doing the same thing (working outside) last summer? If so, she could be reacting to something from outside (like insect bites or contact with a something, or even heat related). But the reaction doesn't really manifest until later. Does she wear a uniform?

Having her switch beds could help solve the mystery.

Chigger bites usually look like a blister and they are unbearably itchy. What are the bites like and is she outside much.

My kid gets a rash that looks like small bug bites from oxiclean. I never use it in my laundry but had used it with rags to clean my tile kitchen floor. He would get the rash when I washed our rags and then washed our clothes after. I had to throw out all the rags.

Also does she sunbathe? This is the first year I get heat rash if my skin is exposed for more than a few minutes.

Chigger Bites! Was your child outside yesterday? Chigger bites typically appear and start itching a few hours after exposure. They look similar to mosquito or bed bug bites. I get them every July after spending time in my backyard or in the woods.

OP here. Thanks for these good ideas. I will sleep in her bed the next few nights and she can sleep in the guest room and we’ll see what happens.

I have cleaned and vacuumed so much in her room I can’t imagine there are spiders (plus aren’t spider bites usually just a few? her torso is covered). I will have to investigate carpet beetles and their bites, although wouldn’t a pest control company have found evidence of these? I’m so stumped.

I should have added in my o.p. that when this peoblem happened last summer, after the pest control companies said no bed bugs, we vacuumed her mattress and put an encaser on it and her pillows (the sheets that we change weekly are on top)

Oak mites?