After Charlotte accepts Mr Collins' proposal, Elizabeth feels a sense of loss -- her friend has accepted a silly man, and Elizabeth is disappointed.
From Chapter 23:
Between Elizabeth and Charlotte there was a restraint which kept them mutually silent on the subject; and Elizabeth felt persuaded that no real confidence could ever subsist between them again. Her disappointment in Charlotte made her turn with fonder regard to her sister, of whose rectitude and delicacy she was sure her opinion could never be shaken, and for whose happiness she grew daily more anxious
Elizabeth has complete confidence in Jane and knows that she will never be disappointed in her. What a lovely sentiment. They were close as sisters and become even closer; they are good friends as well as being sisters -- an example to all around them, though I suspect that few (if any) appreciate them as such. :-)