For most of my life, I nominally supported the Second Amendment, but I probably would have supported restrictions designed to "weed out" people who were "too stupid" or "too unstable" to own firearms, particularly handguns. My few attempts at shooting had left me so frustrated that I while I liked handguns in concept, I disliked them in practice. Putting a few restrictions on them wouldn't have seemed so bad to me.
In 1992, the L.A. riots made me realize that if things went bad, maybe no one could protect me but myself. Unfortunately, I'm not quick enough or co-ordinated enough to be much of a fighter. Furthermore, no one can fight against a group of others without a very effective weapon. I saw an ad for a home safety and handgun course offered through the local adult education. The course was taught at a local police department and consisted of half a day of classroom instruction and a few hours of shooting. The officers who taught the course were good instructors, and I left the course believing that I could learn to shoot reasonably well.
That confidence changed everything for me. Afterwards, I realized that I had a stake in protecting the Second Amendment. In truth, I rarely get to shoot these days, but I spend a great deal of time supporting candidates who support the gun rights.
I don't know whether it would have made a difference for your sister, but I think many people would care more about gun rights if they had a better understanding of guns and weren't either intimidated or frustrated by them.
WFTR
Bill