Hens have been laying eggs, hatching chicks, and raising chicks with roosters and other hens in the flock since there were chickens. In your first post you say this is one of your bantam hens so you do have others. I’m not totally sure why other hens in with her messes things up. Do you specifically want only her eggs to hatch? A hen will hatch any other hen’s eggs, it doesn’t have to be her own. What many of us would do is to leave them all together, then when one went broody collect eggs from all the hens until we got enough to hatch, then start them at the same time. But if you specifically want her eggs that won’t work.
There is debate on whether allowing eggs to pile up will cause a hen to go broody. I think it can help if you have a hen that often goes broody, but I’ve tried it a few times without success. The only time I had a hen go broody when I did that was on a different nest. Sheesh!
Since the hen doesn’t care whose eggs they are, you could just mark one egg a day in the nest and leave those while taking all the others so the number builds up. You may or may not get a broody hen. You probably have a better chance of getting a broody hen this way but it may or may not be the one you are talking about. Does that matter?
If you get so many eggs in the nest that your bantam cannot cover them all you won’t get a good hatch. You can let them pile up all you want until she goes broody, but after she goes broody (hopefully she will) you need to remove any extra eggs so she can cover what is left. If you try this and you want to hatch some of those eggs, I’d write the date it was laid on each egg so I’d know to throw away the oldest. If you collect new eggs to give her when she goes broody that won’t matter.
There are a lot of different ways to go about this. Exactly how to do it depends on what results you want. I’m not exactly sure what your concerns are or what you want to get out of this, other than baby chicks.
Some roosters will help the hen find a good nest, some even help her incubate the eggs but those are really rare. If you just have the two of them locked up in there the odds of him helping increase a little but it’s still rare. One of a rooster’s driving instincts is to make babies. Often a rooster will help a hen raise her chicks, but most of the time they don’t. But it is extremely rare for a rooster to be any kind of a threat to a hen and her clutch of eggs or baby chicks. That’s just not the way it works. After they mate a hen will normally lay fertile eggs for about two weeks, maybe a few days less and probably a few days more. So the rooster does not have to stay with that hen full time for her to lay fertile eggs. You can alternate him in and out if you wish. But once a hen goes broody she has no need to remain fertile. While I doubt he’d cause any problems with her, I’d certainly take him out of the breeding pen after she goes broody. He really doesn’t serve a purpose then.
