Glad your daughter survived her trip! And enjoyed it.
The seed was probably picked up at the beach along with the shells.
It sounds like either a True sea bean (Mucuna species) or Sea purse
(Dioclea species) (both in the bean family). The Peterson Field Guide to
Southeastern and Caribbean Seashores has a picture of the former on p.146.
The best reference for beach seeds is World Guide to Tropical Drift Seeds
and Fruits, but that book isn't as easy to come by.
Thanks for ordering the book. Hope you enjoy it and get to use it
here some day.