Como dizer "Está livre" em inglês

I couldn’t find a topic that “sanasse” my question.

In a few minutes ago, a girl in the canteen asked me:

-there is someone here? (And she “apontou” to the chair)

I replied her so:

-It’s vacant. (I tried to say that she could sit in there)

And she said:

-oh! Really? The both?

And she started to move away, so I realized that she understood that is someone sat in there.

So I called her again:

-hey, no! There is no one in here, you can sit!

So, now, my question it’s. I was right to say “it’s vacant”?

And also, wich sentence or expression in Portuguese would make sense to say “está livre” can I use “it’s free”? What’s the most common?