Create a new document, any size. I used 800x600px. Fill the background layer with black. After that, place your photo in the center of the document.
Select the Polygonal Lasso Tool (L) and select the girl. When you complete the selection process, go to Select > Refine Edge. A dialog box will open with some settings. Select to preview the image on black, and make some adjustments until you find a nice result. Add a bit of feather, radius, and expand the selection. Then