I was on the Wonder the last week of April and trading was almost non existant between guests. They did set up a trading table every evening manned by a couple of CM's but there were very few people trading. There were however lots of CM's with lanyards on so your daughter can trade readily with the CM's that she sees.
There wasn't a dedicated area for Pin Trading during the day like dizneykids referred to that she found in Sept. They might have had that area in September because it was the week after the Disneyana Convention and there were a lot of Convention people on board. The area that they set up at night was simply a small table where a CM sold pins and they had a book you could look through to see their traders if you didn't see anything on their lanyards. They had a lot of cruise pins in the book. I also found some retired Gift Cruise Pins on lanyards. Look for PP#113:
Castaway Cay Palm
BTW..........the CM's on Castaway Cay had lanyards on too. Don't forget to go into the little Merchandise Store and get the Castaway Cay Airplane pin. You won't find this one on the ship or available from WDW Merchandising. That store is the only place you can get that pin. PP #3088: Castaway Cay Airplane
Have a great time...I know you will. We did. There is something for everyone. There were 600 kids on the cruise that we were on and they were kept so busy we hardly saw any of them. I did go to one of the Oceaneers Clubs to check it out (our kids are 20 & 23 but I was interested to see what it was all about) and the kids were having a wonderful time.....they didn't want to leave when their parents came to get them at midnight.
Be sure to look at the CM's in the Port Canaveral Terminal. Many of them had lanyards on and I found a WDW 2000 press pin on a CM lanyard and a couple of other spiffy pins there. That was a surprise. My lanyard was packed but I always keep a few pins in my fanny pack just in case. And I wasn't even looking for pins.

I was the only one who was trading with them while waiting to board the ship. So be prepared. You never know what you might find.
All in all have fun.......the ship is beautiful, Castaway Cay is beautiful.......I know you and your family will enjoy it.