When I was 17, I had a pilonidol cyst and had three surgeries on it within one year, as the wound kept re-opening. We tried packing it, and stitches, but it didn't close all the way. Very frustrating, as you would imagine. I ended up seeking a new surgeon, who did a z plasty, and the wound healed and hasn't opened back up since. I'm now almost 30.
The upside, is that the cyst is gone! The downside, is that I have a nasty scar from the z plasty that I'm considering getting cosmetic surgery on, as it's literally changed the way my rear looks.
I hope your daughter has healed from this.