Yes, I think it will go on indefinitely unless you can remove her from the coop overnight, as well as shutting her out in the day. Mine go to roost soon after 4-30 at the moment, hens always roost at sunset, and get up around 7.00, so they are roosting in darkness for over 14 hours. By the middle of December, this will become up to 16 hours. Your broody will make no progress out of her hormonal state if you just lift her out of a comfy nest box for the few remaining hours of what passes as daylight in midwinter.
If you don’t have anything that could safely become a spare overnight shelter for her out of doors, another way could be to put her in a dog crate, rabbit hutch, or even a cardboard box and put this in a shed or garage, somewhere unheated and airy. Line it with newspaper to catch the droppings, but no bedding, just the flat floor. No food or water is needed whilst she is roosting. Get her up as early as you can to rejoin her friend in the open air so she gets as much light as possible.
At this time of year, you are up against it with providing enough light, although most hens come out of the breeding season when the days get shorter. One idea would be to move her into a cage with a mesh top, in a garage etc with an overhead light left on all the time, as if it was midsummer. This might shift her hormones - might be worth a try - what do other people on here think? Anyone else had a November teenage mum to deal with?
The only other option to making a really determined attempt to get her out of broodiness is just to carry on as you are doing, making her come out as much as possible during the day. This would help her, making sure she is eating sensibly and not getting any broodier, but whatever you do, the situation is pretty certain to happen over and over, and with both of them next year- that’s what Silkies are like!
She sounds quite a character! We would love a photo of her and her friend if you have any.