Does she have a sister??Or get her into shooting. Got the girlfriend into shooting, she's all about me buying ammo and reloading supplies. She's recently realized she like revolvers a lot more than her semi auto, and is all about me accumulating some extra wheel guns.
I find that if I buy a few guns in a short amount of time, I sneak them home and hide them away. I can then introduce them in a orderly manner, a few months apart like I'm being responsible. Or, don't tell them about it til you're selling it, tell them about the profit you're making, and then take a portion of the proceeds to buy something else, saving the extra or buying something for them. they never think to ask where the original gun came from and are excited about the new gun, lol. These are all things that have worked for me.