When thinking about this question, you might find it helpful to relate this excellent novel to Great Expectations by Charles Dickens. Both are written using the same point of view, which is the first person retrospective point of view. This means that there is an older narrator looking back at their exploits when young, and the narration oscillates between the younger narrator speaking about their experiences and then the older narrator stepping in as it were to comment upon their younger selves. This is something that we can see in Jane's account of herself at many stages during the novel. One example is in Chapter Three, when Jane is asked about her living conditions by the apothecary. Note how the older Jane intervenes to give comment at this stage:
How much I wished to reply fully to this question! How difficult it was to frame any answer! Children can feel, but they cannot analyse their feelings; and if the analysis is partially effected in thought, they know not how to express the result of the process in words.
Clearly the way in which the narrator talks about the state of being a child and its various limitations shows us that this is the mature, adult Jane Eyre breaking in to her narrative and giving us a more sober comment on what follows. The novel is full of such examples, and it would be well worth trying to identify a few more cases of such retrospective narration.