Lostdog, hope the following might be useful.
First, I think it might be helpful to read up on women's actual experiences of PND on a less highly charged website than MN.
Second point, many women seem to have an extreme fear of being away from their babies - perhaps your wife found your daughter's illness so distressing it triggered an understandable but very primitive protectiveness that she saw you trying to prevent.
I'm sure you didn't set out to thwart her desire to have the baby in your bed - you probably thought you had agreed on that - "we had her in bed with us which was fine and we both discussed that we would not let her get used to this and as soon as she was better she would go back to her cot".
The problem was, after the illness, the landscape had changed for your wife - whether through anxiety, or tiredness, or a combination. You thought you could get back to the agreement - she didn't want to. You, logical male, thought baby in cot meant better sleep. Your wife had other ideas and this seemed to be the trigger for her change of mood. Is this when the PND diagnosis was made?
Just wondering too, how severe is her PND? Is it possible she needs more intervention thanjust CBT? Also, perhaps you can find a support group for partners of PND-sufferers.