I hope she did not neglect her duty to retreat.
There is explicitly no duty to retreat in one's home in Missouri.
July 3, 2007Blunt Signs Legislation Protecting Missourians Right to Defend Their Families from Attack
CAPE GIRARDEAU– Gov. Matt Blunt today signed legislation he called for in his January State of the State Address clearly reinforcing Missourians’ legal right to use force while defending themselves and their loved ones from attack.
“Americans maintain a deep reverence for their Second Amendment rights. This legislation is an extension of those rights. It ensures law-abiding Missourians will not be punished when they use force to defend themselves and their loved ones from attacks in their own home or vehicle,” Gov. Blunt said. “I commend the General Assembly for supporting and passing this important law for Missouri families.”
The legislation commonly referred to as the “Castle Doctrine” removes the requirement from law that victims must attempt to flee if attacked in their home before they are legally justified to forcefully defend themselves against their attacker. The bill also prohibits criminal charges or civil suits against Missourians who use justifiable force to defend themselves.
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I don't know if there ever actually was a "duty to retreat" in one's home in Missouri (Florida, for instance, passed an explicit Castle Doctrine law a few years ago although its existing Castle Doctrine was not impaired before the new law's passage --- instead, the new law added several important protections from litigation for people who stood their ground rather than removed any non-existent "duty to retreat" which had never been the case in Florida), but clearly there is not one now.
Not in Florida, the GUN-SHINE state!
She should be able to shoot him on the front lawn.