Question: When Alice returned to the real world in the end, why wasn't she taken back to the mental asylum?
Question: How did The Red Queen shrink The Mad Hatter's family into the size of ants?
Answer: She probably forced them to drink "Pishalver" which is the potion that will make one shrink.
Answer: The way I interpreted the scene is that Mirana subconsciously altered her own memory to convince herself that she had not eaten the tart to avoid the guilt of the resulting accident. This is a real phenomenon, so it's perfectly plausible. If my assumption is correct, this scene shows Mirana realizing for the first time that she is in fact responsible for everything that has happened since due to a single lie she told.
Phixius ★