We don't know a lot about this character, but while reading, we feel sympathy for her. She takes Huck to her house, or in other words, under her wing and promises to make him more civilized, which was not exactly what he wanted, but it was a nice gesture.
Miss Watson is Widow and Douglas' sister; she was a tolerable slim old lady with glasses. We can imagine that she was as good as her sister, but no, she’s her total antonym. She was very cruel, racist, and slave owner. Also, she didn’t like Tom.
Widow Douglas and Miss Watson in the Essays