In my Opinion from my experience, taking chicks of a Mother hen who has hatched them herself can not be an enjoyable experience. I tried to do so once and the hen was absolutely devastated. The look in her eyes. I gave the chicks back to Mama and she quit her mourning. You should really let her keep one or two but I understand where your coming from. IF you whish to give her duck eggs there is a good chance she'll stay broody. As long as you remove the chicks as soon as you can otherwise mother and babies become to attached.
My advise would be to let her keep her ducklings (If she hatches them) and see if she can raise them. Duck eggs take longer to hatch than chickens and making her brood another batch after the duck eggs would be plain unfair. Which will also result in a hen that is less likely to go broody again+ A skinny Chook. Brooding takes a lot of their precious foraging and feeding times away.
Best of luck!