I get patches of psoriasis in my hairline, behind my ears and back of my neck. I use and OTC 1% steroid cream on it and that seems to work wonders. Once its gone it won't usually come back for a little while but I have to treat it as soon as I notice the raised dry patches or else they turn into large bleeding scabs which spread down onto my face and down my neck.
All I can suggest is using a really mild shampoo as its on the head so it doesn't get too irritated and don't blow dry the hair - I try and let as much of it as possible dry naturally as I find blow drying dries the patches out more and causes more flakes and makes it more irritated and scabby.
Fortunately mines pretty much under control just by observing when its coming up and using the 1% cream when it does. It can be so sore and miserable when its bad, I hope your daughter's clears up soon.
PS.Forgot to mention sunlight is supposed to help psoriasis, give it a google, one of my friends sisters has it really bad and she has light therapy. Whenever its sunny (rare in England lol) or I go on holiday mine will totally clear up.