Okay, so I don't really mean to suggest that Helen Burns (Jane's friend at Lowood in Jane Eyre) is actually the daughter of St. John Rivers (Jane's ascetic cousin). But it has just occurred to me how similar the two are. And that is a strange occurrence, given that Helen seems more likable (perhaps much more) than St. John.
But just think about the two for a moment. I described St. John as ascetic: the same goes for Helen. Where child Jane is interested in fantasy and trying to find a way out of her lonely, dependent life, Helen absorbs herself in learning, trying to better herself and make plans for the future. And Jane learns a lot from Helen: meeting Helen was probably the best thing that happened to her as a child (unless you want to count getting an education first).
St. John is devoted to the church and to becoming a missionary. I think Jane can somewhat admire his perseverance and devotion, but their opinions come to a parting of ways when he asks her to marry him and join him in his missionary work. She tells him she would be willing to go with him, but does not feel (as he does) that it is her duty/the only right path to marry him and go. So what Jane learns from St. John is, essentially, to rely on her own inner voice and to make her own decisions. Which, coming back to Helen, sounds a lot like what Helen shows Jane.
Jane meets Helen: Jane decides to advertise to be a governess and is thereby able to leave Lowood. Jane meets St. John: Jane decides to go back to Thornfield and thereby learns of the death of Mrs. Rochester and is finally able to marry Rochester. Both are acts of freewill.