Cuckoo Maran chick keeps injuring Color pack

[Esshea]

I got chicks from Coastal a few weeks ago. 2 Cuckoo Marans and 2 color packs. They have been in the same brooder together since purchase and are about 4.5- 5 weeks old.
When I saw the Marans at Coastal there was one who kept pecking the neck of another chick. I didn’t think I ended up with that Maran when the employee grabbed chicks for me but I guess I did
We moved the birds to an extra large brooder until we feel it’s safe to integrate to my outdoor flock. Today I noticed my biggest color pack has been pecked bald and is started to get sores on the back of her neck from said offender.
Do I quarantine the pecker, the pecked or both? I’ve never had an issue with chicks pecking before. I noticed my other color pack had a sore spot on the top of her beak today and am wondering if the Maran is starting to go after her too. Should I release the Maran into my existing flock so she can get her butt kicked? Oh man, what to do.

 

[Justso]

Too bad about the bully! I hope a quarantine will work.
Here's an article I really like
https://www.backyardchickens.com/articles/chicken-bully-chicken-victim-a-two-sided-issue.73923/

 

[Esshea]

So far I have the chick isolated in a pet crate inside the brooder. I might move the other chicks outside with the older birds and keep this one indoors. Mostly I just want to get rid of her haha.

 

[Folly's place]

The older birds might, or might not, help change her attitude. Moving her on elsewhere is a good idea though! Send her oof, with full disclosure, to a flock of older birds...
Mary