'Mum' feather pecking chick

The chick is now 5 weeks old today and a couple of days ago I noticed some of the back feathers (about a inch long strip continued from the tail) had been pecked off. I immediately put some gentian violet on the area, to which 'Mum' pecked and ended up with a purple beak. I noticed her pecking the chick again today. Not a bullying peck or peck of annoyance, but more to peck feathers, because she studied her chick as if to decide what area to peck.

Their run area is 6 feet by 3 and a half feet and the coop area is 3 and a half by 6 feet. Their area is an extention of the main run, which we use when segregating new hens etc, then it is opened up again and becomes part of the main run again. The coop area is also a sectioned off area of the main coop.

'Mum' has never been a feather pecker before, so I'm a little confused. I've let her out with the other hens (without chick) for a little while. When the chick thinks Mum is out of sight she cheeps and Mum comes running back, checks shes ok then gradually moves off again. Mums still sharing tasty morsels with the chick and telling it she has something nice, so shes still doing 'Mum' stuff.

Mum does pace the run when she sees the other hens out on their grassed area of the garden, but I cant let both her and chick out as we have cats and get the odd hawk flying over, plus I wouldn't trust the other hens with the chick.

Sorry to go on for so long!  Thanks in advance.

Thanks  joyful You hit the nail on the head!

Mum and chick did have lice! Sprayed chick with mite spray on the live ones, she had a gathering of feather lice on one feather on each wing and she had a dusting of Diatom (little more than intended as thought the puffer pack was almost empty, but wasn't  ). She went briefly from lavendar to white.

Mum had a good puff of Diatom too and I'm keeping a beady eye on them.