You're right that the full adult plumage won't come in till about 2 years but you can generally tell by the teenage patterns what you have. It's not odd that she hasn't started quacking at this age. I had one that didn't quack till about 8 weeks. It's also common for young hens to have orange legs that darken as they get older. Drakes have yellow bills not black ones and I'm not seeing any green on the head. I'm still going to say Daisy is female.
I'd love to see what Daisy looks like after the first molt and with adult plumage. Daisy is already a beautiful duck.
Oh thank you, you've made my day!! Yes, she definitely has orange legs and no sign of green on her head at all! Fingers crossed that you're right - I'll let you know how things progress. And I'll post some updated pics after her first molt (yes, she is pretty gorgeous isn't she!). Thanks again for your help.