First, I have to say that you treated the wound well.
As for what to do next, I don't think it is a good idea to put the hen back with the flock. The dust/dirt is not a concern, but pecking by flockmates is. Chickens naturally are attracted to strange things, especially the color red, and often times will peck an injured bird to death. One way around this is covering the wound with a colored wound spray, like Blue-kote, since that disguises the color and helps deter other birds. The best option, though, is to keep the injured hen separate at least until the wound has scabbed over and healed a little.
It is true that isolation for a long time can make re-introducing the hen difficult. It is especially hard to reintroduce a single bird. However, there are a few things you can do to minimize reintroduction problems. One thing to do is put another gentle flockmate or two in with the injured hen after a few days. They may fight a little, but at least the entire flock won't be attacking one bird. Then, you can try introducing the several isolated birds in with the entire flock. The attention won't all be directed at one bird, and the risk of injury will be lessened.
Another thing to try is to put the injured hen in a dog crate or other wire enclosure where the flock can see her (and she can see them), but they can't touch each other. Let the flock live within sight of the hen for a few days, and then try introducing her. Hopefully, the exposure to the hen before introduction will prevent a lot of fighting.
Well, I hope that helps. Good luck with your hen!
