She did it before.

The first time Karen Murphy left her son, Ryan, alone in her minivan, a call from day care and cool winter weather saved him. The 2-year-old was strapped into the vehicle alone for less than 30 minutes in January, according to news reports.

The second time Murphy forgot to drop Ryan at day care, she drove to her veterinary office in Northern Virginia and did not see her 2-year-old for about seven hours. Her husband went to the day-care center to pick up Ryan and discovered that he was not there. By the time he called home, by the time Murphy raced out to her minivan on Gentle Shade Drive last month, Ryan was unresponsive in the back seat.

The ghastly fact that Murphy is a repeat offender complicates the question of whether she should be charged with a crime for her son’s death. Prince William Commonwealth’s Attorney Paul B. Ebert indicted Murphy this month not just on charges of child neglect but also of felony murder.

Murphy’s conduct was inexcusable. But as horrendous as the consequences were, the charges against her amount to prosecutorial overreach. In fact, I’m not sure that Murphy, who also has two preteen daughters, should be prosecuted at all. While it is unconscionable that this was Murphy’s second such error, that doesn’t make her behavior a crime.

Ebert has said that he decided to bring criminal charges as “a wake-up call for other people who may be trying to not take care of their children.” He acknowledged to The Post recently that “It certainly wasn’t intentional. . . . But the fact is that she was on notice. This is an innocent child, and she wasn’t up to speed on taking care of him. It gets to the point where it becomes neglect.”

Is Murphy’s case really an example of a mother trying not to take care of her child? And is prosecuting her going to deter other parents from behaving neglectfully? Virginia’s legal definition of neglect is failure to provide food, clothing, shelter or supervision. Murphy clearly did the latter, but in his 2009 Washington Post Magazine story on the heat-related deaths of children forgotten in vehicles, Gene Weingarten explained that even the most “loving and attentive parent” can fall victim to a momentary lapse in memory and leave a child in a car. Prosecuting Murphy isn’t likely to act as a deterrent to such cases.

Prosecuting, or even sentencing, Murphy is also not nearly as likely to affect her behavior as much as her own remorse and heartbreak. The only remaining reason to charge Murphy is to express society’s revulsion. But retribution is a cruel motive for putting a grieving parent through a grueling trial. Perhaps that’s why prosecutors bring criminal charges in only 60 percent of cases like Murphy’s and dismiss the other 40 percent as tragic accidents, according to Kids and Cars, an organization that promotes auto safety for children.

In any event, the charge of felony murder is too severe. Virginia’s legal standards for felony murder require the accused to have had the “intent” to commit a crime and that a death resulted from that felony. In other words, Murphy would have to have intended to neglect her child. Imagine that, on a summer afternoon, a father wants to grab a bite to eat. He rolls down his car windows a notch and leaves his toddler sleeping in the vehicle while he pops into a restaurant. When he returns half an hour later, the child has died. The father was aware that the boy was there, and he acted recklessly in leaving him in the car on a hot day — those actions amount to felony murder.

But Murphy claims that she forgot that her toddler was in her car. This means that she neglected him — but there’s no evidence, so far, that she intended to do so.

After his research into this issue, Weingarten concluded that “There may be no act of human failing that more fundamentally challenges our society’s views about crime, punishment, justice and mercy.” It is hard to determine what kind of parent Murphy is and what kind of treatment she deserves. But it appears at this point that she was a loving mother for whom a lapse of judgment resulted in disaster. For such a woman, one who suffers from no defect of heart or mind, the eternal loss and guilt Murphy is bound to feel are punishment enough.

Molly Roberts is a writer in Washington.