To make it appear to wrap around her arm, I use a layer mask. With the new layer selected, press the layer mask button at the bottom of the layers palette, or go to layers > layer mask > reveal all. Using a black brush, paint out the lights lines you want to be behind the arm.
By the way, to get rid of that pesky path from showing, choose paths from the layers palette and click somewhere outside the selected path. If you want to save the path for future editing, double click on the layer and choose okay. Otherwise, when you start your next path, the first one will disappear.
You are now done with your first PP light painting line.
Make a new layer, new path and repeat the steps for all the light lines you want. Experiment with different shaped brushes and colors.