Complex sentence: When Colvin refused to get up, she was thinking about a school paper that she had written that day about the local custom that prevented blacks from using the dressing rooms and trying on clothing in department stores.
Split into simpler sentences: When Colvin refused to get up, she was thinking about a school paper that she had written that day. It was about the local custom that prevented blacks from using the dressing rooms and trying on clothing in department stores.