Your friend should be able to file a lawsuit in small claims court as long as the amount in dispute is under 10,000 dollars. Small claims court is designed for people and situations where using a lawyer would be to expensive or not possible. Where I am from it is actually discourage by the court for either party to hire a lawyer. Your friend should go to the local court and ask for paperwork to file the claim. She will need to know the name and address (at a minimum) in order to get the paperwork served to the contractor. They will set a court date and the contractor has to show up or he loses and if he shows up and loses then the court should be able to give collection options to your friend. I believe she can even file the claim for more than the down payment for the cost of the hassle and paperwork, etc. So check that out. If the value is higher than 10 grand then your friend might want to talk to a lawyer about representing her and payment to be made out of recovered money. If your friend really does have a case and the lawyer sees that they will likely get paid from that I m sure it would work out.
Call the police and file and report for theft.