What's most odd about "Through the Looking-Glass" is it's almost entire disconnect with Lewis Carroll's previous "Alice's Adventures in Wonderland."
Both happen with the same main character and both are dreams. In "Looking-Glass," Alice is seven years old, probably a year older than in "Adventures." Also, the cat, Dinah, has just had kittens. So a year between dreams is logical.
There is a sea change in Alice between the adventures. In the first, she jumps from being a precocious young girl to being a top-notch problem solver and a legit pragmatist. In "Looking-Glass" she is even more so. She's more like a 14 year old than a young girl. For example, she knows quite a bit of mathematics.
Otherwise, there are characters (the Madd Hatter, the March Hare) who make appearances in the second dream, but Alice does not seem to recognize them. Also, there is little actual reference by Alice to the previous dream.
It all makes sense, really. We have to remember as readers that we are taking this girl's dreams a lot more seriously because they are published in a book. To her, they are fleeting adventures in her sub-concious, probably forgotten after a couple of days.