This site posted “5 Reasons To Get Excited For The Expanse Season 3” and one of them is the new cast members.
This is the part about Liz:
Elizabeth Mitchell, who you might remember from Lost, has also been brought in and should play either Clarissa Mao or Anna Volovodov. Without wanting to give away any spoilers, these are the names of the new female characters in the book series and should have a major role in the third season.
Obviously she won’t play Clarissa Mao.