Yes, she'll set and hatch them. Problem is that chickens will take 1 week less than duck eggs to hatch, and so the duck may not yet want to leave the nest, even though they have hatched. Nature has preprogrammed her to set for a certain number of days. She may go longer if needed, but shorter periods may prevent her from leaving the nest, and the chicks could die from lack of food and water. To be sure, you should determine hatch date and be there to see how she reacts once gthey have all hatched and are completely dry.