She used her car to block Barnes's path after he sped through a checkpoint but was killed before she had a chance to leave her patrol car or return fire.
Barnes, who served in Iraq in 2007-2008 and was a specialist in outdoor survival, allegedly left a cache of weapons and body armour in his own car before fleeing on foot into the woods.
Authorities put the park on lockdown and herded around 125 tourists into a visitors centre where they were forced to spend the day under armed guard. Adults were made to kneel while officers inspected each of their faces out of concern that the gunman may have joined the crowd and slipped into the building undetected.
"That was scary for the kids," one visitor said.
Last night, police announced that they had found a body amid thick snow but could not immediately confirm it was that of the shooter. They did not say whether the person killed themselves or died from exposure to the elements.
The body was spotted from the air lying face down in drainage ditch and authorities needed nearly two hours to trek through four foot snow and recover the corpse.
Detectives said there was a "strong probability" that the body was Barnes's.
Barnes had previously posted pictures of himself carrying an assault rifle and reportedly kept an arsenal of weapons at his home. The mother of his young daughter sought a restraining order against him earlier this year after she became afraid for their child's safety.
According to court papers, Barnes had told his former partner that he wanted to kill himself.
He is suspected of opening fire at a party in Skyway, a suburb of Seattle, at around 3am on January 1 following an argument.
The shooting injured four people, two of whom were last night said to be in critical condition in hospital.