Warm baths
Most children (and adults too!) feel a bit better after a bath. Add a handful of bicarbonate of soda (this can particularly help itching but don't add too much as this could make things worse).
Make sure the bath isn't too hot as this will only aggravate the itching. Feeling too hot makes most itchy rashes worse, so make sure your child isn't overdressed and air can circulate over their skin to keep it cool. She'll be more comfortable lightly dressed in a warm environment than the other way round.