Who's the maid of Helen Keller?

No maid is mentioned in the text. The Story of My Life does, however, mention servants. Helen's nurse is mentioned by name.

I think I knew when I was naughty, for I knew that it hurt Ella, my nurse, to kick her, and when my fit of temper was over I had a feeling akin to regret. But I cannot remember any instance in which this feeling prevented me from repeating the naughtiness when I failed to get what I wanted.