I don't have any idea what color to breed her to. The same she is I would imagine, whatever that is!
Maybe you should post this in the waterfowl forum. You might get a better response that way?
Lavender is recessive, so you would need to breed her to another lavander-then you will get all lav's.
Or, you can breed her to a black, all her ducklings will carry the gene, breed one of her drakes back to her and half of THOSE ducklings (2nd gen) will be lavender.