Severe PND could be the root cause of the lack of bonding. Until that is trated properly, it could be hard for you to sort it out.
I too didn't bond with one of my DC for sometime, and had undiagnosed PND for several years. I bonded with him pretty instantly as soon as the PND was treated. I look at him now and feel confused and surprised that I felt anything else, and also at times terrible guilt.
But as Goosey says, walk the talk. It's the best advice. Act as if. Acting As If is one of the best ways to cope. I went out with my DS alone so we could bond, and I couldn't focus on my other DC instead. It helped a bit. (He didn't seem that keen on me either, from birth onwards, which didn't help! :) ) But gradually we had common memories of good times. Now although he still triggers me in a more volatile way than his brother does, I love him so deeply and massively that it's hard to remember it was ever different.
Even if that doesn't happen, even if you don't bond, you are still being a brilliant mother by behaving exactly as you would if you had bonded. All the stuff you mention - co sleeping, slinging, BFing - that's caring, nurturing, loving behaviour, even if it's secretly a huge effort for you.
One thing I wonder - hope this doesn't sound too psycho-babble - is it because it's DD, not DS? May be harder to bond with a girl if you have strong negative misgivings about yourself, and your ability to raise a girl well if your own upbringing led to mental health problems. If you look after yourself better, maybe you'll feel better equipped to raise a happy, self-confident little girl.
There's often a cause for poor bonding. MY DS was ill for years. Perhaps I was scared he'd die and didn't want to get too close. Our bonding coincided with him getting well. He's also depressive. I recognise the symptoms, even though he's a young child, because I had them. I'm trying to train him to think positively but it's a slog. He's very glass half empty (or emptier!)
Some people are harder to love. Sometimes those people are our children. But if we are conscientious and treat them with equal warmth and nurture and affection and good humour, then that's as good as love. Because many parents who deeply love their kids don't show half those qualities because they don't think they need to, and their kids suffer from the lack. I do believe lots of really good care equals love, even if you don't feel the love. She'll thrive in your care. that's what matters. And maybe you'll bond later - maybe in her teens, or even as adults.
It's OK, you know. It feels like the guiltiest, most evil secret in the world, but it isn't. You treat her well, as if you felt that bond, and that's what matters for her. The love may grow from that. It did for me, and I really hope it does for you, but even before it did, things got easier.