Welcome to BYC!
Put a fake egg in both nests and they will likely use both.
Remove all eggs from nests daily, a truly hormonal broody will sit on nothing.
As long as the Aframe is weather and predator proof it should work great for a broody coop. Does it have a nest similar to the ones in the main coop? If not, get one set up.
Is there enough space for the nest and a feeder and a waterer...and room to poop away from all those things? About 2x2' of open floor space would be minimum, IMO.
It would be good of the broody coop was very close to and in sight of the main coop and run so she can see the flock and the flock can see her during her confinement.
This is how I 'move' a broody hen. Once I
know she's broody for
sure I move her to the broody coop with fake eggs in the nest. They are not happy to be moved to a new enclosure, but if
truly broody will settle down on the fakes eggs within a day or less-usually few hours. Once she's sitting tight again for a day or two, during which time I test her by stroking her face and neck, gently lifting her up to see eggs, to get her used to me checking things out.
Then I give her fresh fertile eggs and start the countdown
Before you decide to hatch more chicks think about.....
My Broody Notes:
You'll need to decide if you
want her to hatch out some chicks, and how you will 'manage' it.
Do you have, or can you get, some fertile eggs?
Do you have the space needed? Both for more chickens and she may need to be separated by wire from the rest of the flock.
Do you have a plan on what to do with the inevitable males? Rehome, butcher, keep in separate 'bachelor pad'?
If you decide to let her hatch out some fertile eggs, this is a great thread for reference and to ask questions.
It's a long one but just start reading the first few pages, then browse thru some more at random.
http://www.backyardchickens.com/t/496101/broody-hen-thread