Replying to Question about U.S. Work VISA

So my girlfriend is having a female friend come visit for a few months. She may stay as long as a year. I told my girl no problem as long as her friend could carry her own, she can stay with us. How would one go about applying for a work VISA? She is from Germany and does have a German Passport already. She would like to come sometime at the end of Summer. How long does this take to file? Any help is awesome, thanks.