Change #2 slightly and it'll be correct. "It was stuffy in the hall so she took off her jacket"

It was stuffy in the hall so she took off her jacket. ---This means it was kind of hot and humid in the hall so she was too warm. She took off her jacket to cool down. There was stuff in the hall and she took off her jacket. ----This means there were THINGS IN the hall, AND she took off her jacket. There is no connection explaining why she took off the jacket. There were things/There was stuff: boxes, papers, pens, dogs, anything. Hope this helps!!