Sounds like a virus...kids can sometimes spike a really high temp at the onset of a tummy bug.
This happened to DS2 one year, he had a very high temp & was in hospital for a day or two before the vomiting & runs set in, then they said 'ahh...that's what it was'
I'd just keep an eye on her, make sure temp stays down now, & she doesn't dehydrate.. it will probably run it's course.
Hope she feels better soon