@Nah because it's part of her plan, she wants to destroy them from the inside out, so if she shows up with her original body it will be much more difficult than with the body she has now Since everyone there trusts the lady, if she appears as Stella the revenge will have to be more brutal and faster, but she doesn't want that she wants a slow and painful revenge so infiltrating with the Enemy is the best option.
Keep your friends close and your enemies even closer.
Keep your friends close and your enemies even closer.