It doesn't matter. She sees one that she thinks is pretty. The best way to seriously piss her off is to tell her she wants a different one. Rationality, logic, etc is gone. She wants THAT Gun.
Best thing to do, show her the one she wants, make sure it's comfortable for her to hold, if she still wants it after holding it, teach her all about it and how it works.
Same goes for real guns. There is nothing worse than going somewhere to buy something (with money) and having someone try and make you get something totally different. You never know too- sometimes it's fun to go somewhere and start gushing over the aesthetics of something without talking about the practical reasons you want it. You get some really fun looks.
Or the reason for buying one thing, is that something else you have is lonely.