The answer to your question can be found at the end of Act One, which charts the first tumultuous meeting of Annie and her new pupil, Helen Keller. Having challenged Helen and having tried to impose her will on Helen, Helen manages to lock Annie in the room upstairs and hides the key. When dinner is served, the only way that the Kellers are able to get her out is by getting a ladder and leaning it against the wall by the open window so that Annie can leave the room and come downstairs, in a very undignified fashion. James in particular is very humorous about this, not revealing why he needs to get a ladder to get Annie down for dinner until he is questioned about it. Annie later discovers that Helen had concealed the key in her mouth, and she watches her as she happily drops the key into the well.
James gets a ladder to help get the teacher out of room who has been locked in by the student who stole the key.