The Australian woman, whose husband works for ANZ in Port Moresby, struck a seven year old girl on Poreporena Freeway.
ANZ said the woman "clipped" the child, but the girl was then run over by another car and suffered two broken legs.
Following the advice of security experts the woman drove off to avoid violence at the scene of the accident on May 7 and reported the incident to police later that day.
She has since returned to Australia to avoid the risk of a revenge attack and is cooperating with police.
ANZ said in a statement that the girl ran onto road without warning because she was being chased by an attacker.
"Clearly this was a terrible situation, and our staff member's wife reacted in exactly the way she was taught by PNG security experts," the bank said.
"All companies operating in PNG instruct their staff and dependents not to stop when in involved in road accidents due to the significant risk of violence and to report the matter as soon as practical to the police.
"This is common practice for both locals and expats living in PNG."
Local media named the girl as Serah Kevin, and it is understood she is due to undergo a leg operation to insert steel plates into her right leg at Port Moresby General Hospital.
ANZ is assisting the girl's family and meeting medical expenses.