Tabitha2, one of my daughter's had a sucking habit. When she was 4, our dentist gave me a book, I think it was called Danny Stops Sucking his Thumb. The dentist advised me to read it to her every night for a week, and tell her at the start of the week the plan was we'd read the book every night, and then she'd stop sucking her nightie/soft toy/fingers etc. I worked like a dream. I was amazed at how easy it was to break a well established comfort habit. When I returned the book to the dentist, he told me it worked every time.
I'll bet if you google, you can find a similar tale. The skin picking needs a stop put doesn't it. Good luck