Being an only duck may be the whole root of the behavioural problems. No matter how much attention we give them, they still need the company of other ducks. They are not psychologically meant to be without their own kind. Humans, or even other birds, cannot replace this for them.
Not saying...
Is she your only duck? If not, how is she acting towards the others?
The yellowing could be caused by the 'waterproofing' gland if she over-grooms. My white Magpie gets this all the time, trying to turn back into a duckling!
As for her actions, she sounds scared of something. Has she been...