If she's not painfully shy, she should be fine. My DS was doing this at about 5. It's a nice way for the kids to get comfortable with cast members (in case they get lost, they'll know who they can approach). Most of the CMs are really good with kids.
And one more -- a PP said that you should try to trade like-value pins -- with CMs, it really doesn't matter. Don't worry about trading a small pin for one that's really fancy. They just got it from another guest, and if you tried to buy big pins to trade for big pins, you'd go broke. But if you try to trade with other guests (which I never really do, anyway), you'd better be trading same value pins -- and guests can turn you down for trades, which cast members generally won't do.
Erin
Even if she is shy, it wouldn't matter. I have traded for many years and have always found that the cm knows what to do. They also haved figured out when someone is looking at their lanyard and they will just show it to you. Anyway you just go up to the cm and just ask if you can look at their pins. The cm's are very accomodating and nice.

