A lot depends on your set up. Do you have a good size run? Do you have clutter in the run? Hideouts, roosts? Multiple feed stations?
What I have done in the past is add chicks about 3 week old to a safety zone inside the run. They have an insulated box, wind protection, but not added heat. They are enclosed and safe from the hens. If you put a box in the zone, they will naturally go there at night. Then you can scoop that up, lock in the coop for safety at night.
After two or three days, I just lift the gate and fencing off the ground 4-5 inches. Big enough that the chicks can get out of the safety zone. I wait with them till one of them gets brave enough to come out, and I give a mock chase and they scuttle back to safety. Near this, I have a pallet laid flat on a couple of rocks or bricks, so that there is a another place a chick can scuttle to safety.
What this allows is for the chicks to explore and retreat on their terms. And generally works very well. Chicks are as quick as lightening, and can outrun most hens, if there is a place to escape to.
Generally, what you need is a place for the chicks to escape too, and hens really don't pay anymore attention to chicks, than junco's. I feed in the safety zone. I keep it set up for two or three weeks, and they work it out.
I would get 3 chicks. They have company and a huddle buddy. With the birds you have, there is a strong chance from here on out, that you may loose more. Often times it is not uncommon for these breeds to die around 3-4 years. I know people post about 8 year old birds, but not real common.
If not, you can always sell a layer or a pair later at point of lay, by then, the pullet will be fully accepted in the flock.
Mrs K