i think making blue/black related now that we know black fairy is Rump’s mom is a bad idea. This show really just cannot make ALL of its cast related. I would have gone for it before we know for a fact black fairy was Mama Stiltskin. But now? Nah. Blue and Black being the same person (in the same way as Jekyll and Hyde) then sure.
Perhaps Blue wanted get rid of her inner darkness to ascend to being Mrs. Great And Powerful Ruler Of The Fairies, and her evil side just did her own thing.
"I could have the giant duck as my steed!" --Daniel Radcliffe
Keeper Of Tamara's Taser , Jafar's Staff, Kitsis’s Glasses , Ariel’s Tail, Dopey's Hat , Peter Pan’s Shadow, Outfit, & Pied Cloak,Red Queen's Castle, White Rabbit's Power To World Hop, Zelena's BroomStick, & ALL MAGIC