She is, by all accounts, the first person to sign on to the project. According to IMDB, Pejić will play Sister #4 — a.k.a. one of Ariel's mermaid siblings.
This isn't the Australian's first foray into acting, though; she starred in David Bowie's 2013 music video for "The Stars (Are Out Tonight)" with Tilda Swinton. She has also appeared in a short film called Reason and a historical television show called Faith. Coppola's project — one that's beginning to pick up steam in the casting department — will be her first big acting gig. The jury is still out as to who will play Ariel, but we've got a few ideas up our sleeves in the meantime. (Daily Mail)