The baby was nearly fully formed with a face, hands, feet, and a heartbeat that could have survived outside the womb. I implore you to go look up some photos of a 28 week fetus and I guarantee you’ll be surprised how much it looks like a normal baby.
You’re right, it’s not Facebook’s business, but this 17-year old and her mother chose to discuss a crime on Facebook’s platform. Facebook had a legal obligation to hand over those messages because they were served a valid warrant.