Hi, Sarah! How exciting that you get to visit what I think is the jewel in the
Disney Vacation Club crown. Aulani is so beautiful and so special - I hope your family has an amazing time.
Everyone who goes on the
Rainbow Reef for the snorkeling will be required to wear a life vest, no matter how adapt a swimmer they are. So not only can your daughter wear one, she won't even feel out of place doing so, since the whole gang will be wearing them with her.
They do recommend that guests doing one of the snorkeling excursions on the reef be good enough swimmers that they can swim independently. As long as she feels confident enough in her skills to be able to swim without assistance, she should be fine. If she feels a little uncomfortable about that, she might enjoy Fish are Friends, which can be booked through
Aunty's Beach House. This allows kids ages 3-12 get a hands on look at the care and feeding of the fish. It's a 3-hour experience, but it's packed with fun and information.
I am so glad you are getting to enjoy this experience with your family. Enjoy every second of the island magic. Mahalo!