Q:

"I'd rather she has' vs "I'd rather she had"

Which one is correct and why?

She hasn't been to Paris. I'd rather she has been to Paris. / I'd rather she had been to Paris.

Thanks.

A:

I'd rather she has been to Paris.
I'd rather she had been to Paris.
The former sentence doesn't sound grammatical, whereas the latter is OK.
Technically, you use would rather + have + past participle when the subject in both clauses is the same person  talking about preferring one thing to another in the past. For example:
I'd rather have been to Paris.
When you have two different subjects in the clauses, you use the past oerfect to refer to the past.  So the  second sentence as follows is correct:
I'd rather she had been to Paris.

