It doesn't look like a rooster to me, but I could be wrong. I was able to tell two of my black australorps were roosters at 4 weeks because their combs and wattles started developing wayyy too fast. As if their appearance wasn't clue enough, there was their behavior.
Of course, some varieties develop faster than others, and the differences between hens and roosters will become apparent at different times and in different ways.
Once the wound has healed it should be safe to put her back with the other chicks. I have to wonder though why your chicks are being so aggressive towards each other. Do they have enough room/food/water? Are they bored?
yes they have all that and i do not know why but the worst are my RI reds, and every time it heals i put her back i watch, they pech, and its bloody. i am a new chicken owner and i dont know if it is infected.it looks like this now.......gross pic sorry