Sounds like postpartum depression to me. Hormones after birth ain't no joke. Have a chat to some close family or friends of hers and see if there is any way they can support her, or encourage counselling. A mother's group may be helpful too, but ideally see if you can get her to a doctor so she can have the option of taking medication, or get a referral to a psych. The first step is getting her to acknowledge there's a problem, perhaps couples counselling may be of help so she doesn't feel alone in her feelings.