Investing in a small wire dog crate might be a good idea, I've found them to be very useful in a multitude of ways as a chicken keeper.
Sometimes you can find them cheap at yard sales or thrift stores.
Having room in the coop to isolate birds, for various reasons, is something else to think about being able to do before enlarging your flock.
If she's still laying and going to roost at night, she may not be truly broody....may be just 'thinking' about it.
I would not put a bird in the broody breaker until I had seen that she stayed on the nest for 3 days and nights, except for daily outings to eatdrinkpoop.
I had a bird isolated for an injury, in that same crate tho it had the tray and some bedding in it, and she laid in there just fine every day.
Clover forgo her morning treats sitting on an empty nest but went outside and was in the run. When the rain began later, she headed for the nest but had not been sitting on the egg because it was cold. She did not lay yesterday. So she may being only considering being broody? It is getting cooler here so maybe the temperature is helping discourage her. She still growled at me when I took the egg. Many thanks. Will check the broody thread. Yesterday too busy...