I had the same problem with my cayuga, she used to hug me, I would take her into my lap and she would lay her head on my shoulder. If she was sitting sideways on my lap, she would adjust her position specifically to hug me, this was normal for her even when she was 3 yrs old. One day a raccoon got in the yard and attacked one of the other ducks (I had 3 ducks) and the whole world changed, the cayuga became aggressive, she would bite me to the point of breaking skin, she behaved exactly as you describe, running away, couldn't touch her, etc. that has continued for the last 2 yrs. A couple of months ago the duck that had been attacked passed away from other issues not related to the attack. Ever since that duck passed, my cayuga has been much better, she still doesn't hug me and she doesn't like to be picked up or caught but will allow it. I can only assume that she was behaving aggressively for those years in effort to protect the one that had been attacked and now she doesn't need to do that. Is the duck that you are talking about the "leader" of the flock? She may be protecting the flock. You may never get your cuddly duck back and trust me, I understand how disappointing it is but I don't feel it is that abnormal. Hang in there and just keep being quiet and gentle around her, offer treats from your hand. Move slowly around her etc. She could come around but I don't think you should expect it. Sometimes it's just how ducks are.