quien and que, which one to use?

Question

In the following sentence:

La mujer ________(que/quien) vimos ayer, es la mujer de Juan.

I chose "quien", although I thought both would be fine according to the explanation in the reference section of SD.

However, the answer sheet says to use "que" with the following explanation:

“Quien” no puede ser sujeto de una oración especificativa.

Is the answer sheet correct? If so, why?

Answer 1

I think "que" is correct.

To use "quien", it should be slightly different: "La mujer a quien vimos ayer, es la mujer de Juan".

Answer 2

I would always say "La mujer que vimos" in conversation if I were speaking to someone. That's just my personal preference.

In English you could say "The woman that we saw was Maria" or "The woman who we saw was Maria".

Answer 3

This is the difference between "who" and "whom". Who would be proper for this sentence, not whom. This is true for both Spanish and English.

You would not say, "The woman whom we saw yesterday..."

You would say, "The woman who we saw yesterday..."