Symbolism, Imagery, Allegory
If you’ve read Game of Thrones then you know that, where there’s fire, there’s also ice! (You could learn that from Frankenstein, too.)
Anyway, not only does Jane take special interest in the images of birds in arctic landscapes when she’s reading Bewick’s British Birds (yawn) as a child, but as an adult she also draws a fantasy landscape filled with ice and snow that seems to have special meaning for her.
When she decides that she has to leave Rochester, she tells herself that she "must be ice and rock to him" instead of letting him know that she returns his passion. Of course, the iciest of the characters isn’t Jane herself, but St. John Rivers, who has an "ice of reserve" and claims that "no fervour infects" him. (Later, Jane tells Rochester that St. John is "cold as an iceberg.")
Jane’s fascination with ice seems to be the result of her hotheaded nature—she herself may seem cold, but she’s actually incredibly fiery and passionate, and she gets really angry about injustice. As a result, she’s mesmerized by all things frozen and icy because she can’t be that way. Her one attempt at icy behavior—rejecting Rochester—results in her meeting St. John, who shows her just how undesirable a cold-hearted approach to the world really is. In fact, St. John’s icy lack of passion seems almost immoral.