Your broody is doing a great job so far, so why would you take her chick from her when she has done nothing wrong. The new chick may well be less safe with the older chicks as they might pick on it and could even kill it. The broody mother will look after it and show it how to eat and drink and in time, forage and dust bath and integrate with the flock and roost. The most pleasure is to be had from watching a broody mother her chicks. Don't rob her or yourself of that joy.
Make sure there is food and water within reach of the nest and that the chick can climb back in if it falls out and leave the broody to decide what happens with the other eggs. Most likely she will stick with them for another couple of days and then if they haven't hatched, abandon them and start foraging with her chick. Of course, they may all hatch and then you will have even more joy.
Good luck with them. I have had over 90% survival rate with my broody reared chicks and of the 2 that I lost, 1 was crushed when a board dropped on it and the other died from an unknown illness. My hens free range with my horses and a feral cat. My first broody had 14 chicks and looked after them exceptionally well and 13 made it to adulthood. Have faith in your broody and enjoy watching nature at work.
Best wishes
Barbara