Starting a new flocks with two different groups

How young are the chicks? A single older bird is going to be driven cranky by those chicks, and she is not going to mother them. If they are real small, she may kill them.

However, because (if I read this right) being as none of the birds have been in your own set up, none of them have home territory advantage. So you might pull it off, with a few tricks of the trade.

I hope you have a run. You need to divide the run, so that there is a bit of shelter in one part, and that part is sectioned off with some woven wire. The openings in the wire need to be large enough that the chicks can get through, but not big enough for the chicken. When you get the set up, put your chicks in the run, and chase them a bit, so they figure out where they can go for safety. Don't worry about scaring them for life. After this one time, just sit quietly in the run, and they will get used to you. Chickens don't remember much.

Another way of giving chicks a safe place is 4 cement blocks, and a pallet laid across the them. This makes for a low to the ground barrier that the chicks can escape under, and it gives them a bit of shade too. I usually put some feed for them under that too. A determined big chicken can get under this, but it really slows them down, still allowing the chicks to escape.

Where ever you are getting the old hen, bring her a buddy from there. A single hen, is a stressed hen, and it will be months before she thinks the chicks are company worth her time. You are going to have two separate or sub flocks until the chicks begin to lay eggs. That is just chicken society.

Good luck,

Mrs K

 

Here's some notes I've taken on integration that I found to be very helpful.......
......take what applies or might help and ignore the rest.
See if any of them, or the links provided at the bottom, might offer some tips that will assist you in your situation:

Integration of new chickens into flock.

Consider medical quarantine:
BYC Medical Quarantine Article
Poultry Biosecurity
BYC 'medical quarantine' search

It's about territory and resources(space/food/water). Existing birds will almost always attack new ones.
Understanding chicken behaviors is essential to integrating new birds into your flock.

Confine new birds within sight but physically segregated from older/existing birds for several weeks, so they can see and get used to each other but not physically interact. Integrating new birds of equal size works best.

The more space, the better. Birds will peck to establish dominance, the pecked bird needs space to get away. As long as there's no blood drawn and/or new bird is not trapped/pinned down, let them work it out. Every time you interfere or remove new birds, they'll have to start the pecking order thing all over again.

Multiple feed/water stations. Dominance issues are most often carried out over sustenance, more stations lessens the frequency of that issue.

Places for the new birds to hide out of line of sight and/or up and away from any bully birds.

In adjacent runs, spread scratch grains along the dividing mesh, best of mesh is just big enough for birds to stick their head thru, so they get used to eating together.

Another option, if possible, is to put all birds in a new coop and run, this takes the territoriality issues away.

For smaller chicks I used a large wire dog crate right in the coop for the smallers. I removed the crate door and put up a piece of wire fencing over the opening and bent up one corner just enough for the smallers to fit thru but the biggers could not. Feed and water inside the crate for the smallers. Make sure the smallers know how to get in and out of the crate opening before exposing them to the olders. this worked out great for me, by the time the crate was too small for the them to roost in there(about 3 weeks), they had pretty much integrated themselves to the olders. If you have too many smallers to fit in a crate you can partition off part of the coop with a wire wall and make the same openings for smallers escape.

Best example ever of chick respite and doors by azygous
http://https://www.backyardchickens.com/t/1069595/introducing-chicks-to-adults#post_16276224

Read up on integration..... BYC advanced search>titles only>integration
This is good place to start reading:
https://www.backyardchickens.com/a/adding-to-your-flock