I am sorry that your hen has suffered a vent injury from pecking. Vent pecking may lead to damaged tissue and later, cannibalism. Once they see red from blood, or perhaps a partial prolapse, they will join in pecking. Some hens may also get some damage from laying too large of eggs. Many times they will get a build up of hard droppings or white urates inside the vent opening. Sometimes in those cases it helps to lubricate the vent and use a gloved finger to dig out any hard material if there is any there. Hopefully with time her vent will heal. I don’t know if you are giving her a warm shallow soak (with Epsom salts or a TB of salt per gallon of water )to her vent daily, but that may help in healing. Just get the vent area and legs wet, and dry her thoroughly. If her droppings are firm or hard, I would give her a tsp of chilled coconut oil daily to peck at and to soften them.