The first thing i did was paint over her hair with a mask to do this press ‘q’
When done press ‘q’ again and select inverse. Create a new layer then fill it with any color then right click on the layer of hair and select blending options, change to soft light. Finally use the eraser were you messed up and went over somthing else.
This is the original picture i did not change anything
For information on how to do this vist http://tutorialblog.org/photo-retouching-change-hair-color/