Helen Keller is initially unable to ask Miss Sullivan questions because she has no way to communicate. Miss Sullivan has been brought in to try to bridge the gap between Helen's world of darkness and soundlessness and the rest of society.
Helen can only react to the presence of the mysterious woman who hugs her and gives her a doll. She doesn't know who Miss Sullivan is or why she is there. As Helen puts it, she is in a dense fog and doesn't realize she is near the safe harbor that Miss Sullivan represents.
When Miss Sullivan spells the word doll in her hand while Helen is holding her new doll, Helen can't make the connection between the letters and the object. She goes to her mother in delight and shows her the letters, but she has no idea what they mean. It is only after Helen understands, later, that what Miss Sullivan is spelling in her hand means "water" that a new world opens to her, and she has a means to ask her teacher questions.