The blood stained feathers will clean up after a few dirt baths, no problem. A mild staining won't attract the others.
Yes, stand by when you place her back with the flock. As I said, you can expect the chickens from the bottom of the pecking order to challenge her, since the order has shuffled since her absence.
One or more of those low ranking hens will probably walk up to her, they will stand motionless for a few seconds, and if it's silently agreed that the returning hen is agreeable to the new pecking order, nothing further will happen.
If, on the other hand, the returning hen doesn't agree to a lesser rank, then the two will flare neck feathers, spread wings, and hop about for another few seconds until one backs down, possible with a slightly bloody comb. This is normal.
If the altercation continues longer than about 30 seconds, you may need to separate the two, but keep everyone within sight of the flock. The combatants may continue to disagree through the barrier fence between them. Leave them alone for a while. Then a few hours later, release the captive and start over.