This version of Lillie is not even Lillie at all, but a Shiny Nihilego disguised as her.  You can tell the difference between normal Lillie and Shiny Lillie by looking at the outfit, since normal Lillie wears a white dress with blue while Lillie the Nihilego wears the same outfit, but with yellow instead of blue.  Despite being a disguised Nihilego, this "fake" Lillie is actually very friendly and social, which is an exact polar opposite to a normal Nihilego's destructive personality.