Hi, poor little chook.
Yes, once blood is drawn chickens get very aggressive and will keep pecking at the site, until they do eventually kill the bird. This is why bird drinkers and feeders are RED, as chickens are drawn to that colour and it encourages pecking!
I would deffo take the little one away until she is completely healed and then reintroduce her later on.
You will find that cockerels do go for the bottom of the pecking order and she may be his favourite, so he will keep chasing her, if that is the case, then Mr Cockerel has to go or the little hen.
I have 2 boys in with my girls, so I got another 5 hens, to even out "snuggle time" haha