Hawaii is stupid expensive, the flight is long and the airfare overpriced. Your child will learn very little about the rest of the world.
If you are where I think you are, Mexico is a short, cheap flight, an entirely different culture (although your kids school probably looks like it's in Mexico) and the food and activities can be very inexpensive.
If you are set on Hawaii, Maui's Grand Wailea is awesome for kids who like to swim. It's a waterpark type resort. Rent a room from a timeshare owner for good prices and more amenities.
On the dolphin thing.
Have her do the swim and just get totally enamoured with the big fish.
After it's over, maybe even later in the day, talk with her about the deplorable conditions and life they have.
I know it sounds like a mind fuck but it's a great lesson for someone that age. That things aren't always as they appear and there are sacrifices for the purpose of entertainment.
Maybe, just maybe, her generation will be able to put an end to this "caged for profit" practice.
If you decide on Mexico, I'm happy to assist. Although I have been all over Mexico, I will speak on Cabo only since I can give relevant, timely advice/info.