She is 24. She is an adult. You won't be able to tell her how dangerous a gun is. You can't even show her. You have to put the info there so she learns it herself. Remember how you were? But I think you got it.
I would disagree about showing her, I have 17 yo daughter, and a couple of you-tube videos of objects being blown to bits was a pretty good start.
My next step is to take her to an outdoor range and do the same thing live, milk jugs, water bottles, fruit, vegetables.
Most people(~70%) are kinetic learners, meaning, they learn by doing. When you see these objects blown to bits, it's not hard to imagine something similar happening if you shoot an animal/person.