1. Open the image to be edited in PSE 9 Editor. Create a duplicate copy of the background layer using Control+J or dragging the background layer to the new layer icon in the layers palette( 1st icon below the layers).
Select the background layer in the layers palette and click the new layer icon which is the first icon in the layers palette below the layers.
This is how the layers palette should now look like. There appears a blank layer between the background layer and the background copy.
2. Now click the top background copy layer in the layers palette and press Control +G or select Layer>Create clipping mask.
See the top layer gets indented in the layers palette indicating that a clipping mask got created.
Change the blending mode of the blank middle layer to Linear Dodge(add). You can do this simpley by selecting the middle layer in the layers palette and changing the blending mode from Normal to Linear Dodge(add) from the combo box in the layers palette.
3. Now select the brush tool from tools bar. Keep the default colors in the color swatch(black and white as default).
Choose the brush size from top bar as 60px of soft mechanical brush type.
Change the Opacity of the brush to 20% from top bar. Remember if the hair color is not not dark as shown but some lighter color, reduce the opacity to half this value(around 10%).
Keeping middle layer selected, start brushing over the area of the hair you want shine to appear.
Here is how my initial and final images look :