I've asked my friend if she could take action with a firearm to prevent injury or death to her kids, and she said "I guess, I don't know...What if god tells me Im a murderer on judgement day??"
zombieslayer, for that one, if your friend is a Bible-believer, you can point out that the "man after God's own heart" (King David) killed more people than almost any other man in the Bible. God did not judge him
for his righteous actions that protected God's people even at the cost of other lives. Rather, He praised him for them.
Edited to add: Also, whether or not she's a Bible believer, you'll probably have better luck starting a bit further back. Don't start with the use of a firearm. Start by asking, "What would you do to defend your children?" and explore that topic very gently for a bit. You will often find that someone who would not be willing to use a firearm to protect their children would be quite willing to do other things that could be equally deadly. In which case the hangup, no matter what the surface appearance might be, isn't really
over deadly force at all.
Further, even the most strongly pacifistic will express willingness to "call the police," knowing that the police are authorized to use deadly force if necessary. Is it really
more moral to command someone else to kill on your behalf, when you are unwilling to do it yourself?