Pin trading is popular at Disney. Pins can be purchased at the parks, but they can tend to get expensive. You can also purchase them on ebay, but you need to be careful of fake pins. I know there is a list of approved sellers somewhere on disboards.
All castmembers at Disney parks wear lanyards. The ones wearing green lanyards can only trade with children, while the ones wearing yellow lanyards can trade with anyone. You simply walk up to a cast member and ask to look at their pins. Since they are wearing the pins it is good to not touch the pins. Then if you find one you like, you take one of your pins and exchange it for one of theirs. There are special "hidden mickey" pins that you can only get by trading with a cast member. Cast members cannot refuse a trade unless you have an obvious fake or non-Disney pin. You can also trade with other guests in the parks, but I have never tried that.
Pin trading is addictive and a lot of fun! You may just want to get her 5-10 pins to trade!