First, I'd start with having a conversation with your step daughter about why she finds firearms frightening. I think before you can bring her around and have any chance at changing the way she perceives firearms, she will first need to feel that you understand where she is coming from and that you respect her feelings. This is probably going to be a process that has to play out over time, so I wouldn't necessarily jump into this next part on day one, but as you discuss firearms and begin to explain why you feel it is important to own them, I would relate it to the fear she has. You can point out that one of the primary reasons you own a gun is to protect her and everyone else in the home from people who do not respect laws or the wellbeing of others. You might want to relate it to something simple like stealing - theft is against the law, but people obviously do it all of the time anyway. Similarly, if everyone always obeyed all laws, there would be much less need to for protecting your loved ones, but unfortunately the "bad guys" are going to break laws, and if they are the only ones with guns, things go sideways pretty quickly. So you could ask her what makes her more afraid: living in a house where there is a gun that could be used by someone who loves her to protect her, or a being in a house where there are no guns when a "bad guy" with a gun breaks in and has bad intentions. You could even cite a few recent examples from the news, such as in Toronto where the police have begun to encourage citizens to leave their car keys on their front porches overnight so that car thieves do not attempt to break into residences to steal the keys, because most Canadians do not have firearms to use in protecting themselves. As the conversation develops over time, you can extend it explain the real reason for the Second Amendment (which is obviously to guard against a tyrannical government), which the founding fathers had just recently escaped and had no desire of finding it necessary to do so again in the future. I was able to navigate that discussion with my own daughter by relating it to her being forced to do things she doesn't want to do, using taxation as an example. I broke it down in terms that she would understand, such as doing jobs around the house in exchange for money, but then only receiving a small percentage of that money due to an onerous "tax" that she had no say in. She did not like that idea at all and saw that it would be unfair, so I explained that is an example of tyranny, and that is what our founding fathers recognized as a very real danger when they set up our form of government. They knew from both studying history and from firsthand experience that if a government feels it can opress its citizens without pushback, it will eventually do so. However, if a government has to continually be mindful that if it pushes its citizens too far, they could revolt (and by doctrine, would feel not only the right but the duty to do so), then that government is much more easily kept within the limits prescribed by its founding documents/constitution. I don't think this is going to be a "one and done" conversation, but I've found that kids can be persuaded on many topics when you respect their opinion and can frame your rebuttal in ways that they can easily understand. Sometimes a mock example can make an ambiguous situation feel very tangible to a child. Good luck.