Autumn's your best bet - breed her to the blue drake. Use a resulting blue male, which will be split to chocolate, and breed him back to Autumn. 25% of the ducklings from that breeding will be blue fawn :)
The way White works is, one copy of white makes a duck pied. Two copies makes it solid white. So, in order to produce solid white, each parent has to be at least pied (carrying one copy of white). Of course the parents could be white as well, but they would definitely have to be at least pied...
Solid white?
That doesn't make sense, given that blue fawn bred to white should yield all pied ducklings only. If she's white, then her mother must have been pied or white. Your original duck that's pictured doesn't appear to be either - which means she can't have been the mother.
That's not...
Yes, but I have to know what color this duckling you're taking back is. If it's blue, that makes everything MUCH easier.
I know it must be pied, but I have to know what color pied - blue pied, black pied, etc.
Oh, if the duckling you're getting back isn't blue, then with your drakes, you still have all the building blocks available to create blue fawn, it's just going to be more complicated and how you'd want to go about it depends on what color this female duckling you're getting back is.
So you're looking to breed back to blue fawn/lilac - aka chocolate with blue?
Well, the chocolate from your original duck Violet would only pass to male ducklings, so if the duckling you're getting back is female, then she doesn't have chocolate, which means you need to use your drake carrying...