While nothing is certain, some insiders say she might be playing the romantic interest of Scott Lang (who is being played by Paul Rudd). Another article from The Hollywood Reporter states that Lilly's role is "not intended to be a one-off appearance." Perhaps this is a hint that she is The Wasp? But nothing confirmed as of yet.
Famous for her roles in LOST and more recently, The Hobbit, Lilly has been in the scene for quite awhile. Lilly is also a Canadian-born actress, originating from Alberta. One of her first roles in film was as a police officer in The Lizzie McGuire Movie. How things have changed.