Answer: B. She realizes her life has changed significantly.
Explanation:
Lyddie is a very determined person and she can see how much her life changes day by day. Therefore, even if yesterday is just one day ago in the past, it feels like "years in the past", because she changed so much.
People can change in an instant and even though just one day passes, the effect of certain moments can be huge on someone's destiny. "Yesterday seemed years in the past" is a metaphorical way for the author to highlight the changes the character has gone through.