The general problem is indifferent to the extraneous person's origin, as long as the truth about it can't or shouldn't be used/revealed, but...
Suppose, a group of teenagers see a meteorite hit the ground and find an alien pod. They move it into one guy's barn. One way or another they interact with the pod; the pod grows and eventually use their DNA to birth what is essentially a group's daughter, who emerges as a fully formed teenage girl, the rest then wither into dust. For at least any superfluous examination she's a human, at least bodily.
If I would be writing this, I would make her a militant nudist just for kinks, and perhaps make very persuasive/manipulative (her true motivations forever suspect), but wouldn't endow her with any fully fledged telepathy or mind control powers, at most maybe suggestive influence upon skin to skin contact. Even as the pod should have some such to some extent, as it needs that to extract as a minimum language skills from the support group (and why not then the rest of their knowledge base and wider understanding of the world to an extent).
The lead guy is of course smitten by the alien girl, and the rest of the group adores her too, and there's of course valid question of how much under her influence they are.
That's all good, but there's the pesky problem, our new girlfriend can't forever live in the barn. At some point she has to be introduced to the parents. It would be fun to even take her to school, right under the nose of shadowy government(?) agents that may or may not be lurking around. But then she should be recognized as a person and gain some documentation upon her.
A possible cop out could be if she took appearance of a missing kid, presumed dead, or otherwise pretended to be a relative (what she somewhat is, technically), but either comes with it's own can of worms and requires a tailored pretext.
(Yes, I'm taking loosely inspiration from a movie titled Encounter, but that was... well if anything, it ended right where it became interesting, even if impossible to resolve in a not totally terrible way, and the take as described above has little resemblance left.)