I love this scene for a lot of reasons:
1) Chibiusa is bored and already knows this story likely because her mother read it to her a million times. Even when she’s queen of the world Usagi STILL loves the story of Sleeping Beauty.
2) Usagi is reading Chibiusa a bedtime story and letting her sleep in her bed and that is just the most endearing thing.
3) There’s a reason why Usagi loves this story. It’s kind of her story, only in reverse. Mamoru was Sleeping Beauty and she was the Prince. Back when she first awakened as Princess she woke him up miraculously. And then there was also the almost kiss in episode 46. Which just recently made me wonder– if she had kissed him, would he have woken up? Would the power of the Silver Crystal then have been used up reviving him again, rather than sealing the evil of Queen Metalia? And the reason why she decides she can’t kiss him and find happiness by herself is because of that?
4) It’s foreshadowing not just to what happens later in the episode but to the fate of Neo Queen Serenity, who is once again basically in the position of Sleeping Beauty. (actually, the crystal encasing her is more reminiscent of Snow White but that’s pretty much just a variation of Sleeping Beauty so)