Schuler's son Bryan was the crash's only survivor and suffered two broken legs and a broken arm, among other serious injuries.
Thomas Ruskin, a private investigator whom Daniel Schuler hired to look into the accident, said Schuler looked "completely" normal when she stopped at a convenient store to purchase Tylenol or Advil hours before the crash.
Investigators had hoped that as the crash's sole survivor, Bryan would be able to shed light on the minutes that led up to the crash. But the boy has not said much, Ruskin said.
"He doesn't seem to remember right now," Ruskin told "Good Morning America" Oct. 16. "He is 5 years old and he is recovering from very severe injuries; fracture plus head trauma he suffered as part of the injuries at the accident.
"He is a miracle child, there's no question about it," he said.
Ruskin said he is now running his own tests to determine what happened that day in hopes of piecing together the moments that led up to the crash.
ABC News' Rich McHugh contributed to this report.