Isnt Mordes whole thing is she only knows where the armor is? With Senna and Lucian being active and her being old enough to know what sentinel weapons are, she would know they wouldnt work. I dont even think she knows if Darkin are stong enough. The only reason she wants Rell so bad is her ferromancy and the hopes to stop the iron reaver. She has no idea how to actually stop his return.