I have psoriasis, have had it since I was pregnant with my son.
Firstly, there are a number of different types, the most common one being plaque psoriasis, which i presume is what she has. There are a few different food things, one common theory is that dairy and wheat makes it worse in some people, so if she wants to she could try cutting out dairy, if no improvement cut out wheat too.
Another theory is that people with psoriasis have problems producing vitamin D3, so many sufferers take D3 supplements (different to just D) at a high dose (5000iu daily).
A good place to get advice and support and suggestions for alternative treatments etc is Psoriasis Help
Psoriasis Help Organisation - Online Psoriasis Forum - Home
There are a lot of bogus alternative creams, pills, lotions and potions out there and when you're at the start of psoriasis it can be easy to see any suggested miracle cure as something you need to try. I went through them all lol, including drinking silica gel (disgusting), and smearing myself with uddermint (a moisturiser for cows udders). None of them worked
There are also a large number of medical treatments, ranging from mild creams, to immuno-suppressants (side effects include coma and death) so a dermatologist can talk her through options and start at the bottom and work up. Unfortunately, I've tried all I can, which is limited because of my health problems (for example, I can't have light therapy which is one of the common treatments) and none have worked, so these days I just live with it.
Stress makes it worse in most people, there is no way to avoid that. Some people who have stressful lifestyles try things like yoga and meditation to try to counteract it.
Psoriasis will often also target damaged skin, so I have developed it on 3 of my 5 keyhole scars. It also affects the nails in some people and can be frequently mistaken for a fungal nail infection.
Hope that helps anyway, I'll stop waffling!