> But if you take Webster’s definition, alien is still overbroad.

That it could perhaps encompass other meanings than the intended one does not make it incorrect for the intended meaning.

> 'Stranger' only describes persons and so is still the appropriate word in the context.

"Stranger's" would be more specific than "alien", and wouldn't be a bad translation, but "alien" is likewise not a bad translation (and, actually, has almost exactly the same breadth in English as "étrangère" does in French; so its arguably the most exact translation, since it uses a word that both admits the specific sense intended within its scope and which has a pretty similar breadth of association as the source.)

Its also the idiomatic word in English for describing something which provokes a feeling of distance from the speaker in a way which is quite appropriate for the subject matter, so its probably the best translation idiomatically.

Overbroad? "Étranger", in French, is just as broad as "alien". It can be used for people, places, things, and more. Save for the ET meaning, any use of "alien" or "foreign" can be translated to "étranger", and vice versa. It is a very broad word.