Sounds like they were clean and I've forgotten how rough some juvenile feathers can get. She should mini molt into some fresh ones before too long at her age still and be as beautiful as her flock mates again!
Here is a decent article that has some photos and descriptions just for reference..
https://the-chicken-chick.com/poultry-lice-and-mites-identification/
Your flock is in good hands, thanks for the update!
