What should I do for my friend to help her through postpartum depression? Any suggestions? Gifts etc?
She needs professional help as well as emotional support from her friends and loved ones. Check in with her often, even if she doesn't respond right away. Visit when you can, bring a meal with you, offer to do things like take care of the baby for half an hour so mom gets a chance to shower and change clothes. Encourage her to see her doctor and/or a therapist specialising in postpartum issues, and show your support when she does things that are good for both her mental and physical health.
She doesn't need gifts. Just be around, offer to help with the baby or other things if she needs time out and listen when she needs to talk. If she can't talk to you about it offer to look after the baby while she speaks to a counselor. There are counselors specializing in this available by phone if she can't physically go and see one.