My 3 year old daughter has a pws that covers most of her left cheek. We always put a cotton mitten on her left hand before she wakes after the treatment as she tends to rub her face for the first hour or so after treatment and we don't want to risk any scratching with her nails. She doesn't seem to have any problem with itching after that, although we do use aquaphor for about 14 days after treatment to keep the treated area moist.
All the best for your daughter's first treatment. It really does get easier after the first one.