As a military wife she probably gets uprooted regularly and has no chance to ever build any sort of relationships with people off-base. It's never that simple.
That's true, but if this guy does this again (and he will, soon), and the daughter dies, the OP will absolutely go to jail too. For a very long time. Probably longer than if she blew the guys head off
Yeah, maybe not permanently leave him necessarily, but remove the daughter from the situation until she can guarantee the gun will be kept properly in a safe. You wouldn't let your kid play in a field with a land mine. This is a similar situation.