Is it too obvious to presume the parasite was Lash?  As we learned from White Night the areas of his brain in which she was stored were destroyed, but given that they were only small bits all over the place and that wizard cells create identical copies when healing she could have returned by now and be tweaking strings out of shot.  Furthermore as a parasite it is within her best interests to keep her host alive.

That was my initial thought as well. The parasite being Lash