I have an Ariel theory. It seems that a lot of Enchanted Forest characters have dealt with a mermaid — Rumple mentioned it about the ink; Regina mentioned it in “Skin Deep.” The promo shows Ariel in Storybrook, but then the producers said she’ll be in Neverland. They also said she’ll have a connection to Storybrook that’s a surprise.
So my theory — I think mermaids have the ability to travel to other worlds without the need of a portal…by diving in the deepest depths of the oceans, they can reach another world. There is no way a non-mermaid could survive such a trip and, thus, everyone else needs a portal. Perhaps Ariel was preoccupied with humans enough to explore other worlds whereas most mermaids just stay in their home in Neverland? She probably has seen/visited the Enchanted Forest and Storybrook many times and encountered at least Rumple and Regina.
Perhaps she is connected with transporting things from GOAT to the “Home Office”?