Love2laugh, firstly, congrats on your coming wedding - and I too think you sound like a great parent - and partner, too, since you seem to show great insight into the situation.
I think it's possibly a combination of your dp being a bit jealous/threatened by your obviously close relationship with dd - especially as you and she were alone together for several years before he met you, and as she has no relationship with her father. Also, as you've said, your dp never learned to be the sort of modern, affectionate father we now expect. His pattern was a disciplinarian, Victorian type. He needs to unlearn this pattern, and you sound as if you're willing to help him do this.
As for your dd, she sounds great! Perfectly normal, very well adjusted, and she shows such maturity in her attitude to your dp. Given this, I'm sure it'll do no harm to explain to her that he might seem hypercritical and unresponsive, but that it's not her fault, but that of his upbringing. It would be terrible for all of you if you let this split you up.
I had a reverse situation when my exh and I split - dd was 10 and understood that my current dp was involved. She absolutely hated him and me with all the anger and pain that a 10 year old has - as she understood what had happened, but not the reasons behind it. It took a great deal of patience and love - and time - to win her round, and dp and I spoke to an excellent family counsellor who supported us (she wouldn't speak to anyone). Now she's 15 and we're living together, and like your dd, she and I are able to talk quite frankly about those years. She said her biggest fear was that I was putting dp first. She no longer feels that and even defends him to my exMIL who's very curious about him and asks her questions that she really shouldn't.
Meanwhile dp admires my relationship with dd, though he occasionally admits to feeling a bit jealous and afraid that I put her first. Luckily he also understands that this isn't reasonable of him, and after all, HE is the adult. But it takes working at .
Hope things go better with you - I really think, from what you've described, that dd and your dh-to-be will be ok in the long run.