Miriam has only taken this form twice in her life. In the past she had no ability to take her true form despite the awakening of her blood, as much as an emotional response learned from her mother. Understanding that despite regaining this form it was tainted by the negative wavelengths of the abyss, thus learning how to truly control it pointing to what has changed; no the Penumbra, but magik itself. It was becoming more poignant she believes while the Penumbra grew complacent or over the long years had been weakened by it.