Eh... I don't agree with not messing with her.
If she's
really broody, she'll stick no matter what.
I like them getting used to me checking things out,
saved a chick whose neck was tangled tight in mama's breast feathers because of it once.
I also put them in a separate part of coop behind wire so the other birds don't lay there and it frees up a regular nest and don't give them fertile eggs until I
know she accepts the new nest.
Are you
sure you
want her to hatch more birds?
You're in the middle of building more space and probably don't need more birds at this point, plus another learning curve to navigate with managing a broody hen and chicks.
Things to think about:
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? 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 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
If you don't want her to hatch out chicks, best to break her broodiness promptly.
My experience went like this: After her setting for 3 days and nights in the nest, I put her in a wire dog crate with smaller wire on the bottom but no bedding, set up on a couple of 4x4's right in the coop with fed and water
I let her out a couple times a day(you don't have to) and she would go out into the run, drop a huge turd, race around running, take a vigorous dust bath then head back to the nest... at which point I put her back in the crate. Each time her outings would lengthen a bit, eating, drinking and scratching more and on the 3rd afternoon she stayed out of the nest and went to roost that evening...event over, back to normal tho she didn't lay for another week or two.
Feed and water added after pic was taken.