Hi there,
I've had psoriasis since I was 16. Mine is relatively mild, I think, but I have patches over my torso, tops of legs, arms, scalp and very occasionally tiny patches on my face. I can at times look a bit like a red dalmatian.
My dad has it, though his is the classic elbows and knees large patches (which are known as plaques).
I think it is unusual in children. It's a funny thing, and can just go away of its own accord. The skin, when treated, can be a bit red, but that does disappear as the plaque disappears. Mine responds very well to sunlight, so if I want to treat it then I go out in the sunshine (with usual UV protection). I've had hospital UV treatment once or twice, which was great, but I didn't do it until I was in my late 20s. I've never had any scarring at all - the plaques can bleed if you scratch them, simply because they don't build up a protective layer - it's not like normal skin bleeding.
I know that you must be worried, but it can be mild and easy to live with. It's so much a part of who I am now that I think I'd be sad if I woke up and it was gone, strange to say. I hope you find something that helps you and dd keep on top of it. The Psoriasis Association may be able to help.