I Evolved her from a Duoblade into an Aegislash at Lvl. 37 (dumb Move, should have waited for Sacred Sword), anf now she is currently at Lvl. 45, amd has yet to learn the signature Move. I'm aware that I can go to the Move Relearner in Dendemille to Learn it, I am asking why she hasn't Learned it Leveling up....
Probably because you evolved it at level 45. You should of waited until doublade was level 51-55. It will learn King's Shield and secret sword at the same time so that is why it didn't learn king's shield. You can also do to the move relearner to remember it if you want to.
Like most pokémon that evolve with an evolution stone, Aegislash doesn't learn any moves by levelling up. Only method now is the Move Relearner.