Make a date night of going to the range or attending a class. Take her to a NICE dinner after shooting - something much nicer than usual as a bribe. Most of the time people who hate guns are scared of them because they haven't been educated, so being around them and learning is an eye opener.
You might also want to familiarize her with things like avg police response times and the sorts of real world crime that go on in good neighborhoods around you.
She isn't likely going to change her mind overnight, but you can work on it step by step.