Hen with bare patches, not healing

One of my hens has two raised bare patches on her back, when I got her last October I presumed it was damage from a cockerel and would heal in time. Six months on it's still the same, in every other respect she is healthy and happy, but she looks such a mess bless her! Any suggestions?

and it may not grow back properly until she moults again, but keep her covered with something like the purple spray already mentioned or Ukadex or tea tree oil in vaseline