I like the idea of it being Andi, although I assume Mouse would be able to tell if something is wrong with her Nfection-wise.
@KSG
Thomas being Nfected is an interesting theory & you make some good points, however the events of TC would refute most of them. If Nemesis is allied with the Black Council (& it seems like they are), finding Morgan wouldn’t have been so much trouble with an Nfected Thomas.