So I was watching Rise of The Guardians for the second time last night, and as it was getting to the scene where Jack recovers his memories, I had an epiphany.
Baby Tooth.
The only Mini-Faerie with the gold feather on her head that becomes Jack’s little companion?
She’s his sister.
Notice the strategically placed  beauty mark.

And Jack’s sister?

They did find each other in the end! So for those of you who didn’t know before - now you do.

Order of the Phoenix Trivia

• The radish earrings worn by Luna Lovegood were made by Evanna Lynch.
• During the breakfast scene in the Great Hall, boxes of cereal can be seen with the names Cheeri-Owls and Pixie-Puffs, with color schemes similar to those of Cheerios and Sugar Puffs boxes, respectively. 
• Harry’s, Ron’s and Hermione’s signatures for the Dumbledore’s Army roster are the same signatures seen in the US version of the books. 
• In the scene where Harry, Ron, and Hermione are discussing Harry’s kiss with Cho, the three begin to crack up near the end of the scene. This was all real laughter from the three actors. The director thought it was good for the scene and kept rolling. 
• J.K. Rowling provided over 70 names for the Black family tree tapestry, complete with details of relations between each and every member, whose were to be scorched and so on. 
• The character of Nigel was created strictly for the movie; he does not appear in the books. However, he combines elements of Colin and Dennis Creevey. 
• Daniel Radcliffe can’t tolerate contact lenses, so in the scene where Harry is possessed, his eyes are digitally changed.
• Originally the death of Sirius Black appeared just as it does in the novel, with Bellatrix pushing him through the death archway after a longer one-on-one duel. Though filmed, the sequence was cut due to time and pacing issues. A portion of this original death scene remains in the final film: when hit with the killing curse, Sirius inexplicably floats backward though the arch. 
• Harry’s scream at the Department of Mysteries was cut out because it was too agonizing.