Mrs. Someone was a fable that first appears in Fables 25.
A witch, formerly of the 13th Floor, who stayed with Briar Rose and Hakim during the takeover of Calabri Anagni in order to protect the Fables' secret weapon against the Adversary and the Snow Queen. Her true name is still unknown as she keeps it a secret "tucked away where no fell power can discern it."
Recently, Briar Rose was carried out of the city by goblins, before the city was burned to the ground. While its not seen, nor is it stated, its assumed that she and Hakim were killed in the fire.