Good Morning, C.. So sorry to hear that your little one has hives! And, from my experience with hives, I am certain that is what she has. Hives can be caused by something she ate, that she usually doesn't eat, by any new laundry soap, or bath soap/shampoo that she hasn't used before or by stressors. If something occurred that was stressful to her. They do spread and are likely to even get on her scalp. You can take her to the doctor and they will give her a steroid shot, which will make the hives disappear within about 30 minutes. They are not viral, so they are not contagious. She is okay to go school, however, if they continue to spread, I would suggest taking her to the doctor. They generally are also very aggravating because they itch and the more they spread, the more they will "raise" on her skin.
I notice that you are a sahm christian mom. I have been looking on Mommasource for other christian moms to network with; learn some new arts/crafts/hobbies to do with other moms. Especially this time of year, as my husband is an avid deer hunter, so I'm a "deer widow" for the next few months and really, really need to meet some women to do some fun things with! Let me know if you are interested in learning a new art/craft, of if you are creative yourself (I don't have a creative bone in my body!) so, I'mlooking for a way to learn something new that is fun!
Good luck and let me know how it goes.
God Bless,
S. Woodall