Upon reaching the Eighth Square, Alice discovers a large crown upon her head—she's now become a queen. However, the crown is big, awkward, and something that Alice has to get used to. This, combined with Alice's unsatisfactory experience as a queen, suggest that being an adult isn't as great as it might seem at first. Alice is just as lost in Looking-glass World as a queen as she was as a pawn, suggesting that the crown—the signifier of queendom, or of adulthood—is nothing more than a signifier. Adults, Carroll suggests, are just as lost in the world as Alice and other children are.
Alice's Crown Quotes in Through the Looking-Glass
So she got up and walked about—rather stiffly just at first, as she was afraid that the crown might come off: but she comforted herself with the thought that there was nobody to see her, "and if I really am a Queen," she said as she sat down again, "I shall be able to manage it quite well in time."
Everything was happening so oddly that she didn't feel a bit surprised at finding the Red Queen and the White Queen sitting close to her, one on each side: she would have liked very much to ask them how they came there, but she feared it would not be quite civil.