One of our RIR's has gone broody, she's had five chicks hatch in the last couple of days and she's still sitting, thank goodness (since there are more eggs). I also have some sort of bantam my neighbor gave me, she got knocked up by my RIR rooster and went broody, she had fifteen eggs but left...
I keep the birds in the coop for a week or two before I let them go out. Then they get used to the coop and want to go back in. Have you tried that already?