Hi Mimi. Welcome to ehealth forum.
As someone who suffers from variouis skin problems (eczema, hives, seborrhea, sensitive skin) I can sympathize. You're a great sibling to want to help your sis. You can do a search of the term psoriasis by typing the word in the light blue search box at the top right of the screen or go to the Skin forum by clicking on the Health Forums tab at the top, scrolling down to Conditions & Diseases, and clicking on Skin.
Your post here is fine but for future reference, Post a Topic is located to your right in a yellow box. It looks similar to the Post a Reply box shown below. You simply click on Post a Topic, give your post a topic which clearly identifies what the issue is, type in your question and click on Submit. (For example, to ask a question about Psoriasis you could simply title it Psoriasis treatments).
Once again, welcome to ehealth forum. I am happy to meet you.