Let's be real, this is simply the reverse of all the people who dismissed the treatment of George Floyd because he'd done crimes in the past, dismissed the treatment of Michael Brown because he'd done crimes in the past.... etc. etc. etc. etc. etc. etc. etc. And trust me, search my handle and you'll find I'm no leftist. I just don't like double standards and hypocrisy.
I also work for a prosecutor's office and while this is an unusually brutal assault, I wouldn't call it strange to charge a 15-year-old as a juvenile in an assault case -- I assume that is the charge, and not attempted murder or something. I'm in a different jurisdiction but usually our attorneys won't even consider certifying a defendant as an adult if they aren't at least 16 unless it is murder or attempted murder.
This is a disgrace, the girl should have been tried as an adult and put in prison for a long time. It is clearly attempted murder to smash an unconscious persons skull into the concrete 4 times.
This goes way beyond "assault" - Look at how seriously the other girl was injured, she had to get 2 surgeries on her skull/brain:
"Gain spent a month in the hospital followed by two weeks in a rehabilitation center. She is still undergoing physical and mental health therapy and will require at least one more surgery to return the portion of her skull doctors removed after her brain swelled, her lawyer Bryan Kaemmerer told 5 On Your Side in May."