She sat in the chair. No problem with that. Woman walked over and decided to occupy a chair.

She was sitting in the chair. She is sitting in the chair. She did sit in the chair. She has been sitting in the chair. She had been sitting in the chair. She will sit in the chair. She will have been sitting in the chair. I'm sure there's other examples.

But using sat or stood or any other past tense verb with the verb to be, nope, not what I was taught.

She was sat conveys the impression that somebody picked her up and plopped her in that chair.