Welcome DBarr, sorry to hear your dw is suffering from PND. It's tough having a baby and so life changing that many struggle just like me to adapt to a complete lifestyle change.
We have a private Facebook group that maybe you or your wife could join. It's a lot quicker moving that the thread here these days. It's completely private and none of yours or your wives RL friends would see anything what we post.
Maybe it would be good for you to suggest your dw joins us. There's quite a few of us who are and have struggled and we offer one another lots of support, advice or just a hand holding reassurance. If she can't talk to RL friends or family she can chat to us, and we've all become good friends now and have meet ups too.
I would have gone insane without the Facebook group as my relationship broke down wen my dd was 10 weeks old and the girls offered me lots of support advice and kind words. there is a whole bunch of us with none sleeping babies too.
Mention it to her, it's just nice to hear and see people going through the same thing and makes you realise you are 'normal'
Re slings, my dd hated hers, but lots of our ladies on the fb group love theirs.