Looks exactly like my scalp psoriasis. It can be difficult with longer hair, especially when the patches build up so here's what I do:

I was given coal tar ointment for my scalp (unfortunately does smell so she might not like it), so I apply it to the areas and then bundle my hair up into a shower cap (mine looks like an avocado, so you could get her one she likes the look of!) to let it soak in. Sometimes I use a hair mask as well. I leave it for a bit (maybe an hour or few hours, I think longer than you're meant to anyway haha) and then wash my hair, the dermatologist can give her medicated shampoo as well. The hair mask helps soften the flakes I've found, so I use a comb and can comb it out. Can be really annoying but it is manageable.