I think that's because they combined Anya with one of the Horizon Labs people from the comics. And to be fair, they needed to change her anyway to remove her original Arana origin.
Quote Originally Posted by Gaastra View Post
You have been watching jayshockblasts videos huh? My nieces love SC and her comics and play her in the lego games. They will love this movie. Kind of shocked we didn't get moon girl as well.
Including Lunella would've meant only Karnak being missing from the current Secret Warriors comic book team, so her omission is a little odd, yeah. Maybe they have separate plans for her.