There's another thing about female violence that often goes unnoticed, which is killing without brute force, specifically poisoning. Poisoning is statistically much more likely to be enacted by women than men. Such deaths are frequently attributed to natural disease, even when the frequency should make it obvious that something else could be going on. One example that comes to mind is the murderous nurse Jane Toppan, who murdered dozens of patients in medical facilities and in families where she worked as a private nurse. Only when she killed 4 members of one family in a weekend, with relatives becoming immediately suspicious, did she attract attention as the mass murderer she turned out to be.

The other category of women murderers who are surely underreported are those who kill their own children. Those who are caught are treated very leniently because they "must" be suffering mental problems (which probably leads to their being counted as committing manslaughter, or mentally unfit to stand trial). Those who disguise poison or pillow-over-the-face murders aren't counted as murderers, and their children aren't counted as murder victims.