The fact that Queen Mallow loved sewing things by hand for her subjects and that the magical "mother's sword" was a needle makes a lot of sense when you learn that in the human world, Mallow's mother did the neighbors' mending. When she died, Mallow took over that job.
When September and Ell meet Lye, Lye seems certain her friend, Mallow, will return, even though Ell says that most people believe she's dead. Lye brought Mallow back from the human world and watched her leave to become the Marquess. Of course she knows her mistress is alive and could return one day.
The girl born in the month of May was named September. And who was traded from Fairyland in her place? A Changeling boy named Hawthorn, who was born in September. But what's Hawthorn? It's one of the trees of the Celtic Tree Calendar... and it represents the month of May.
It is only when reading the prequel, The Girl Who Ruled Fairyland for a Little While, you recognize at some point, how low Mallow has fallen now and how horrible it must be for those who know them both.
More of a Fridge-Tear Jerker, but knowing who the Alleyman really is makes it much sadder, when you consider why he ran away after September screamed at him and said she hated him. That was his own daughter saying it to him, after all.
The third book had one that acts in-universe as well. When September, Saturday, and El learn that the previous fairy inhabitants of the world were transformed into various tools and implements, they wonder whether or not the fairies remained sentient... until September remembers, to her horror, that not so long ago a giant's tool told him "No" and refused to work for him.