Alerted to a medical emergency at the dental office next door, registered nurse Chelsea Moriartey grabbed a crash cart and ran to help.
As she rushed into the room, she saw a small girl lying on the floor.
Dr. William Mather was holding a mask over the girl's mouth.
His registered nurse, Tasneem Ali, was "performing what appeared to be compressions," Moriartey testified.
The final witness called by tribunal counsel at the dental college hearing into Mather's alleged professional misconduct, Moriartey, who is also a CPR instructor, said she instantly realized the other nurse was using the wrong technique.
"She's not an infant," Moriartey said. "Get out of my way."
Mather has pleaded guilty to three of five charges of professional misconduct.
"I dropped down to where Tas was positioned and immediately began two-handed CPR compression," Moriartey testified, wiping away tears.
Moriartey told the tribunal the two-finger technique the other nurse was using is only appropriate for infants aged one year or younger.
She also expressed frustration with the other nurse's inability to quickly attach defibrillation pads.
"It just felt like everything was taking too long," she said.
CPR training scheduled for later same day
The little girl on the floor, Amber Athwal, was rushed to the Stollery Children's Hospital by ambulance at 12:46 p.m. on Sept. 7, 2016.
She suffered permanent brain damage after being deprived of oxygen.
Moriartey told the tribunal she was scheduled to deliver CPR training to Mather's staff that same afternoon at 2 p.m.
"Dr. Mather came down to our office to ask me if I still planned to go ahead with that," she testified, "and I told him that he needed to talk to his staff.
"I didn't think it was appropriate, and I didn't think any of them would be prepared to do that after the events of the day."
The tribunal has been told that Mather never held a staff meeting in the aftermath of the incident with Amber.
Nurse Tasneem Ali testified earlier that she was back at work with another patient that afternoon at 2 p.m.
Mather, 68, who retired as a dentist earlier this month, is expected to testify in his own defence on Monday.