1. Help your wife get as much sleep as possible. If she is breast feeding, she will probably feel sleepy just after nursing. Encourage her to take a nap. "Sleep when the baby sleeps." Once nursing is well established, begin giving your daughter some bottle feedings (ideally of pumped breast milk). This will give your wife a break, and be a special time for you.
2. Get your wife out of the house. Even brief breaks (especially if it's time the two of you can spend together) can be very restoring, especially if you get outside.
3. Surprise your wife with your thoughtfulness. Whatever is special to your beloved, go out of your way to make it happen.
4. Release your wife from as many of her usual roles and responsibilities as possible. Unless she genuinely wants to (and her doctor okays it), she shouldn't have to cook, do dishes, write thank you notes, make love, take out the trash, feed the dog, deal with her in-laws, or anything else except baby care and self-care. If you are not fortunate enough to have paternity leave, it may be difficult for you to pick up all these extra household tasks. (Even if you do have paternity leave, you may be so sleep deprived yourself that you can't do them all!) If that's the case, get help from someone your wife trusts and finds relaxing to have around your home. At the same time, help your wife to realize that she is not marginal to the household. She is an incredibly important person!
5. Your sending a question shows that you are already taking action on behalf of your wife and daughter. Continue to follow that instinct. Get as involved as possible in caring for your baby. Specifically, ask your wife what she would find most helpful. Would she like you to change more diapers? Read baby care books? Call your pediatrician with questions? Rock the baby to sleep? Run out and buy supplies? There is almost nothing that most new mothers appreciate more than concrete, loving assistance from the father in caring for their baby.
6. Shower your wife with praise and encouragement. Point out to her the things that she is doing well, the ways that she is becoming more adept at baby care, the magnificence of what her body has done in creating a new life. Let her know that you believe in her capacity to be a wonderful mother. Gently remind her that it's normal and fine for motherhood to be an unfolding process. 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.
If your wife can't sleep (because she can't, not because the baby won't), if she doesn't want to eat, if she loses interest in life or feels hopeless, if she is having disturbing or suicidal thoughts, or if the blues are lasting more than a week or two, this might be more than postpartum blues -- she might have true postpartum depression.
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. Relax. Pamper yourselves. Enjoy the little things. When life seems particularly hard, take comfort in knowing that this time will soon be over. Though life will never be the the way it was before your daughter was born, soon things will settle down. In the meantime, remind yourself and your wife that this is a once in a lifetime experience that you don't want to miss.