This same type wound happened to one of mine. I have a bit of a different situation, as mine was with over 50 other birds. I put him in a wire cage, right in the coop.
I started letting him go outside with the others in small increments 3 or 4 days later when the wound was drier, but only when I could watch. They had grass etc to forage around in, so they didn't pay him much mind. I thought the fresh air and sun would be beneficial on the wound.
Once the wound was dry and feathers fluffy again, a little over a week later, he was able to go back with the others without me babysitting. The feathers covered pretty well by then.
The wound will ooze for a few days and then scab over. Sometimes it will ooze around the scab if it gets dry and cracks. It will shrink up daily until there is just a thin scar line after the scab comes off- took about 2 1/2 weeks to heal completely. I used Neosporin 2 times a day at first, then once a day til scab was off.
Since you only have the two, it won't matter as much if her sis did forget her I wouldn't think. It's worse when you put 1 stranger in with a lot of them, and the one gets ganged up on.