I really appreciate the additional information you have given us, Iflyglow.
I have read the report and I have watched the video several times.
I agree with you, something seems to be missing in the puzzle.

There were so many people watching both planes coming for landing, including organizers and tower controllers, and nobody communicated or signaled any alert.
Specially when no tandem landing was scheduled.

The pilot of the rear plane was much more experienced than the pilot of the front plane.
Simply, he was certain that he was landing alone, he announced the landing, and nobody told or signed him what was going on.

The report states that the pilot of the front plane took a shortcut in approach and that his canopy was open and noisy enough as to prevent him from listenning the anounce for landing of the rear pilot.

I imagine it was something traumatic for your daughter to witness.
All very sad.

Beck's short biography:

http://www.ndac.aero/images/beck.pdf