Thank you for your query,
could be due to a viral cause.
Continue to give sips of oral rehydrating solutions to prevent dehydration
For rash you can apply calamine
lotion externally over skin for the soothing effect.
Monitor her hydration status by her activity and urine output.
If she is having any signs of dehydration or rash is progressing ,consult the Pediatrician
for examination and for medication.
Hope i have answered your query.