Every body has their own way... here she would be owl, raccoon.. or some others nighttime predator dinner in short order. In other words yes predators look in trees.
I suggest using some treat or other training method to herd and lock them in at night until she sets a routine. Say right before you know she is gonna head that way. Meal worms are popular. I won't use scratch... but whatever works for you AND your birds. They aren't all motivated by the same things.
It usually takes a couple days or a few... For ME... I would be happier with her inside. I don't wanna have to climb a ladder if I need to treat or check for anything.
Some have found their coops are too dark, keeping the birds from heading in. By adding light inside for a few days while the birds recognized they need to get in before the sun disappeared, they easily sat a new routine and were able to eliminate the dusk light permanently.
As a last resort, I would move her in at night after she settled down and lock her in... again until she get's the point, a few days maybe. Most the time they rather go in than be handled.
I will note that roost time antics can be chaos so maybe there is another bird she is avoiding? They usually learn to go in a little sooner or later when that is the case. And it always good to note the possibility of roost mites buggin'... which I don't actually suspect in this instance.
If you can afford the loss and it won't bug you and aren't worried about the elements... free in the trees is a personal choice.
A little training can go a long way towards happy keepers as well.
Hope this is helpful.. NN were great birds when I had them. Very hardy, calm, confident, human friendly, and entertaining.
