So your intent is to integrate the Momma hen and leave the chicks separated, either forever or until you decide to integrate them later.
I've had broody hens wean their chicks at 3 weeks, I've had some not wean them until almost 3 months. When she weans them she abandons them, leaving them in their own. If they try to get too close she may peck them to drive them away. It sounds like your hen has not weaned them yet.
Your chicks are still going under her at night. What are your overnight lows? Can the chicks survive those low temperatures? If they can survive those low temperatures you can lock her away from the chicks and she should break from being broody within a few days.
If the flock could see her while they were separated she may be able to rejoin them without any issues. I'd try that first. Just let her out and see what happens.
If your chicks can handle the low temperatures at 4 weeks they can manage themselves in the run. So when you can try that is dependent on the weather.