On question 2: Yes, a 5-harm handgun is legal. More than legal, it's marvelous. Embrace it!
Even 3-harm without armor is always fatal to an NPC. 5-harm is always fatal even to an NPC wearing 2-armor. To have a chance in a fight against this battlebabe, the NPCs are going to have to cower in armored cars and shit.
To a PC wearing 2-armor, 5-harm is a serious threat: one shot to 9:00, a second shot to midnight. This is a battlebabe that even a gunlugger can't ignore.
By building a battlebabe capable of 5-harm this way, the player is saying that she is just that fucking serious. It's great! Don't try to prevent it or take it away from her. It's not your job to keep NPCs alive when she wants them dead, nor PCs from taking harm when she inflicts harm on them. Follow the results of the moves and when they call for characters to die, let them die.
-Vincent