This really looks like official artwork. Maybe Lisia will appear in Sun and Moon?
Well... if you look at the parent post, you'll notice that it was posted 10 months ago, what was actually even before Sun and Moon was announced... so, based on this image, she won't appear, but like Kafuka-san said sometimes "the possibility exist" (despite being very low at the moment). My hopes are for Shirona-san to show up in Alola at some point.
PS: And despite this looking like official artwork, it isn't (so we can't guess based on it anyway).