Is その彼女/彼 correct in speech?


その人 is a common thing to say but その彼女 feels off. If it's always incorrect,
what about そんな彼女?




In English, "the she", "this you", "such an I" and so on are always incorrect.
In Japanese, you usually don't have to attach その to 彼女, either, because 彼女 by
itself always refers to someone who is already in the "universe of discourse".
However, Japanese person pronouns are basically just nouns, and it's not
ungrammatical to modify them with その, そんな, etc. You can naturally say その彼女 and
そんな彼女 when you want to add the nuance of "such a person" or "the (very) person
(I/you mentioned)" referring to her.

>   * 彼女はアニメが嫌いですが、(その彼女/そんな彼女)が「君の名は。」は絶賛しています。  
>  She does not like anime, but _even she_ admires _Your Name_.
>   * 私はヘビースモーカーでしたが、(その私/そんな私)でも禁煙できました。  
>  I used to be a heavy smoker, but even _the person like me_ could quit
> smoking.
>   * その彼の名前を教えてください。  
>  Please tell me the name of _that (very) guy you mentioned_.
>

In addition, 彼女 is also a normal noun meaning "girlfriend", so saying
something like 太郎とその彼女 ("Taro and his girlfriend") is fine.

