Has she been to any mother and baby groups?
My wife struggled with PND with our first and mostly it was due to having certain expectations of what having a child would be like, worrying about them hitting certain milestones etc.
Attending groups with other parents helped her to realise that everyones children are different, they don’t all sleep perfectly, they change on a daily basis and it can be a struggle to know whether they are doing the right thing.
If your lucky too your local childrens centre will host the groups and will have healthcare workers who can help to support you and your wife. Your doing a great job in reaching out, hope that you can get the he lp you and your family need