(CNN) -- Home alone with her 3-month-old son, Sarah Dawn McKinley of Blanchard, Oklahoma, said she decided to make a stand when two men tried to break into her home on New Year's Eve.
McKinley, who had been widowed less than a week before, placed a couch in front of one door and went to the bedroom and put a bottle in her baby's mouth before calling 911, she said on HLN's "Dr. Drew" on Wednesday.
A 911 operator calmly spoke with McKinley, who asked if it was permissible to shoot an intruder, officials said.
"I've got two guns in my hand. Is it OK to shoot him if he comes in this door?" asked McKinley, 18.
"Well, you have to do whatever you can do to protect yourself," dispatcher Diane Graham responded. "I can't tell you that you can do that, but you do what you have to do to protect your baby."
In the end, McKinley fired a 12-gauge shotgun and killed Justin Shane Martin after he entered her residence, according to a Blanchard Police Department affidavit filed in court Wednesday. Martin was armed with a knife, authorities said.
"You have to make a choice, you or him. I chose my son over him," McKinley told CNN Oklahoma City affiliate KWTV.
First Assistant District Attorney James Walters told CNN that McKinley will not be charged because she acted in self-defense.
"A person has the right to protect themselves, their family and their property," Walters said.
As for the 911 operator's guidance?
"I would agree with that advice," the prosecutor said.
Graham was the first of two 911 operators to speak with McKinley.
The dispatcher told HLN's Jane Velez-Mitchell on Wednesday she learned in training that she could not tell a caller to shoot someone, "(but) as a mother, I wanted her to protect her baby."
"She did a very good job in keeping her (McKinley) calm," Grady County Sheriff Art Kell said of Graham. "Her job is to make sure the person on the phone is comfortable ... to give them support."
McKinley was on the phone with a second dispatcher when she pulled the trigger.
McKinley's husband died Christmas Day of cancer, Walters said. Evidence indicates Martin and Dustin Louis Stewart, 29, may have been looking for painkillers or other drugs taken by McKinley's ill husband, Walters said. Investigator found no such drugs, he told CNN.
McKinley said she believes the men were coming after her, rather than intending to commit a robbery.
According to the affidavit, the men approached McKinley's mobile home Saturday afternoon. Martin had devised a plan to burglarize the residence, police said.
Stewart told investigators he and Martin ingested hydrocodone about 30 minutes before reaching the rural home, the affidavit states.
Martin "aggressively" knocked on the doors of the home and gained entry by hitting one of them with his shoulder, police said. Stewart said "he heard a gunshot after Martin entered the residence," and Stewart then "fled on foot."
McKinley said she had pushed the couch against the door to deter entry.
"When he busted in the door I saw something shimmering in his hand," the mother told HLN. "I thought it was a pistol at first, but it was a 12-inch hunting knife. I didn't know (that) until after I shot and killed him."
Martin, 24, was found between the door and a couch with a knife clutched in his gloved left hand, police said.
Stewart was charged with first-degree felony murder, Walters said. If during the commission of certain offenses, such as burglary, a death results, an individual can be charged in the death, the prosecutor said.
Kell said Stewart is in jail, with a bond hearing scheduled for Thursday in Chickasha.
CNN's calls to police in Blanchard, about 25 miles south of downtown Oklahoma City, were not immediately returned Wednesday.
Stewart's attorney, Stephen Buzin, told CNN he will seek bond.
Buzin would not comment on specifics of the case against his client. "We will let the facts come out at trial and feel comfortable with his innocence," the attorney said.
Martin recently had approached McKinley's home, saying he wanted to introduce himself, Walters said. The man said he worked for the owner of the property on which McKinley lived, she told HLN.
McKinley, also armed with a pistol, was on the phone with authorities for 21 minutes, Walters said.
"She remained as calm as one could under the circumstances and had the forethought and called 911, as everyone should," he said.
McKinley was asked on "Dr. Drew" whether she regretted shooting Martin.
"No. We could have been in a whole different situation if I hadn't done it," she replied.