I can understand the family's statement about being at peace.
Since the service will be held at a Church of Christ, I am assuming that their spiritual beliefs would mean that they realize that Breeann's body is dead, but her soul has moved on. She is now with Jesus, where there is no fear, no sadness, no pain.
The Bible tells us that once we accept Jesus as our Lord and Savior, we are assured a place in Heaven. This would mean that they can look forward to being reunited with Breeann when they die and go to Heaven.
I've put this in very simplistic terms, I'm sure that others could explain it better.
I can only imagine how hard it was for them, not knowing for sure if Breeann was really dead or if he might have left her alive somewhere, or sold her to traffickers! I too, am relieved to know that she is not still suffering!
I am not trying to speak for the family, I don't know them at all. I'm just giving some reasons why they might feel at peace even though their precious child is dead.
JMO
Her funeral should be a celebration of the joy she brought to her family during her short life on Earth, and a time of praise to God that the moment she died, her soul was wisked away from all of the evils of this earth, to live with the angels!