I too have been diagnosed with this skin condition although I am adult. It is really distressing for me so you certainly have my sympathy for your grand daughter.
I have been fortunate enough to be able to consult a dermatologist privately and the end result is that I have been prescribed NEOTIGASON capsules, (Acetretin) - or Vitamin A.
Apart from the redness and itching, I found the flaking skin, hot and general peeling to be worst. I have used numerous creams and lotions and all have had a slight healing effect although I am convinced time has been the greater healer. To date and after two years, I have just undergone UV light treatment since my dermatologist started to lean toward a PSORIASIS diagnosis. As I write, I am clear but keep taking the tablets and am monitored every 4 months.
In my opinion although it has been denied by all medical 'professionals' my problems began after Radiotherapy for breast cancer in 2004 and I am convinced that is what triggered mine. (but that is a different story).
I wish your grand daughter luck.