As many have posted - don't make it 'forbidden fruit.'
My daughter's 14 now, and has been a part of my shooting culture since she was 8. I took her to the range, did NOT let her shoot.. got her to understand that yup, daddy's gun can be kinda loud... and yup, it's pretty messy after it shoots. range time was kept to a minimum, more as an 'exposure' thing than as an educational thing. The firearms were not locked up - but then again, she was living with my ex, so it was never an issue. When she was over, the weapon was in my night-stand, and she knew that it was loud and dirty - two things she wasn't really fond of.
She's big for her age, always has been (5'8 at 14 years old, now) - when she was 10, she towered over most 12 year olds around us. I took her to the range, because she wanted to go shooting. She loved it.
Afterwards, though.. I took her out to the back 40 and showed her what happens to a melon about the size of her head when it gets hit by 147 +p... and told her: I don't want this to happen to you, so now we're going to set some ground rules."
She loved shooting... so the deal is - whenever she's with me, and she wants to, we'll go to the range. The catch? If she ever lays so much as a finger on a weapon when I'm not around, and/or I haven't expressly told her it's okay.. she will never.. ever.. EVER go to the range with me, ever again.
We've never had any issues, not a single one, in the past 6 years.. She's a well-behaved (as well as any 14 year old girl can be, anyway) kid who has a healthy respect for firearms.
I'd strongly encourage the same.
Were she living with me full time, odds are I would have locked up the weapon if I wasn't carrying it, until such time as she was old enough to be able to fire it.. but all in all, my educational method seems to have worked out quite well.