Methods to get the most hatches out of one broody hen?

[fly12]

Recently one of our cochin hens has gone broody and is sitting on 6 duck eggs that are now 3 days until hatch. She has only been broody for 14 days now because the eggs were in the incy for 11 days before she went broody. Currently in the incy are 3 duck eggs that are 15 days old. If I swap the eggs and then when they are 3 days to hatching, take them and hatch them in the incy. I will then buy a few chicks and sneak them under her so she knows her broodiness acomplished something. I want to do this because recently our rooster and ducks were stolen and I want to keep her broody for a bit longer because if she comes out of broodiness she'll be alone and she for some reason never accepts day old chicks and pecks at them. A good plan?

 

[Den in Penn]

Since it seems your going to brood the ducks your self anyway. If you want to keep her broody till it closer to 21 days put some dummy eggs under her, or store bought eggs till you get the chicks.