My assessment after watching video of HER going through the school is that she was well practiced in the handling and deployment of her weapons.
I can’t believe only 6 died.
I think she practiced.
I think the school staff barricading classrooms upon hearing the shots at the front door helped. Also, the time she spent watching for and shooting at arriving LEOs is significant.
She said she liked to binge on video games - probably first person shooter games. I imagine one can LOOK like they know what they are doing from that, youtube videos and an hour or two at the gravel pit.
I read where the staff and kids got into their secure class rooms and followed their training. The 6 people that were killed were caught out in open spaces (hallways, etc.)
I wonder if she tried shooting through the classroom doors trying to gain entry? (Like she did the front doors.) That would use up a lot of rounds.