Adiela, welcome aboard! Your daughter sounds an awful lot like my daughter! She, too, loves dolphins and anything that has to do with dolphins! So, I have the perfect Port Adventure to recommend for you.
During your port stop in Nassau, there are two different dolphin swim locations, but my favorite is Blue Lagoon. You'll see they offer both a dolphin swim and a dolphin encounter. The swim is a bit longer and more involved and for older guests, but the encounter would be perfect for your little dolphin lover and an adult, or the whole family.
The Blue Lagoon Island Dolphin Encounter is for guests starting at age three, so it's just right for your daughter. My daughter had the time of her life when she and I got to swim in the water with Laguna and Gussie Mae, two of the dolphins at Blue Lagoon. Dancing with them, petting them, and even getting a kiss from them was truly something we'll both remember forever. Plus, we since we booked the earliest time for this adventure, we had all afternoon after our swim was over to stay and enjoy Blue Lagoon Island. There are multiple return times back to the ship from the island, so you can play your day the way you'd like and stay longer or head back early. Also, if only you and your daughter want to be in the water with the dolphins but the rest of the family wants to watch and then enjoy the beach day with you, they can book the less expensive
Blue Lagoon Island Dolphin Observer adventure to join you for everything except getting in the water with the dolphins! It's a nice option!
Atlantis Resort offers a dolphin encounter too, but in my experience, we got more interaction time with the dolphins at Blue Lagoon. Have fun planning, Adiela!