Believe or not, but this is entirely normal. Brutal, perhaps, but normal in chicken society. Each chicken in the flock has a rank from top to bottom. Usually, when an individual challenges rank, we don't even notice because the conflict is over so quickly.
Occasionally a conflict can be extended when the two parties refuse to accept the outcome. They keep at each other until one backs down. The comb is the main target for this physical dueling. And as luck would have it, it's rich in blood supply, so bleeding can be profuse.
Blu-kote can heal as well as help disguise the wound to prevent further pecking. But do not separate this hen from the flock. You will only make matters much worse for her when you return her as she will have lost the rank she fought so hard to obtain.
Watch her as you return her to the flock. If she's at the very bottom of the pecking order, there should be no one to bother challenging her. If she aggressively goes after another hen, you will know then that she is challenging the next in rank in order to move up from the bottom.
On the other hand, if several hens converge on her when she's returned, beating the crap out of her, then you will know that she's the victim of bullying and not normal pecking order skirmishes. If she flattens herself to the ground, and they all stand on top of her, you definitely have a serious case of bullying and victim, and you need to intervene.
Come back and let us know what happens when you return her to the flock. I have some advice for handling the victim of extreme bullying if that turns out to be the case.