I'm not saying that it's a major problem, just that it's one of the many things within the film that makes no sense. Sure, she's thousands of years old and could make herself assume the identity of the person she's going to possess...but why? What purpose would it serve? It's not going to make said person any more receptive to being possessed or really make any sort of notable difference.
They could've easily hid her face & made her a lot more Wraith-esque like what we saw for half of the final battle with the Squad.