Chicks pecking one very agressively

[CheekyGirls]

I have had my hens for over a year and are ex-bat hens, so are about 2.5yrs old. They have always got on so well but today Violet is pecking at Lottie, so I put Violet back in the pen area (to cool down). Then an hour later I let her out and Lottie is now pecking at Violet! so Lottie was put in the cooling off area! They are both out now and Lottie is still pecking at Violet and Violet is now hiding on a low hanging tree branch (all feather fluffed up and making a calling noise). Dorrie who his my other hen is ok and neither of them is pecking at her! They should already have established their pecking order! help what can I do? I'm worried when I put them away later in their pen they wont be able to get away from each other!! I'm just going to have another check on them, see if they are made up yet.

Hens all slept together but Violet still in Hen coop when I went to see them this morning and she let out a shrill noise when I lifted the box lid to see her, scared? I have separated then this morning but now they are back together. Violet is all fluffed up and making a warning noise and Lottie is still chasing her. Dorrie has given her the odd peck every now and then. Don't know what to do, can anyone help?