She doesn't have to have all the answers. Over time she will be amazed at how skilled she will become in understanding and nurturing her child. Seek professional advice right away. Her obstetrician or family doctor is a good place to start. Don't let anyone brush this off.
True depression is much less common than the blues.
Professional treatment is important, and is usually quick and effective. Whether your wife's situation is the blues or full blown depression, don't minimize it. The weeks following your child's birth are different from any other time in your life. They are rich, complex, and often out of control. So take a deep breath.