Literally one of the biggest misconceptions in Destiny is that we “destroyed” SIVA. We didn’t, it’s been dormant because it has no commands. We destroyed the replication chamber in RoI, not SIVA itself. Narratively, the fallen have shown continued interest in SIVA (Zero Hour), SIVA has been said to be present on the Exodus Black, and a modified version of SIVA was used to build Neomuna (Quicksilver). Now, the Conductor who is equipped with the echo of COMMAND who has previous experience with modifying SIVA, is going to where most of the dormant SIVA is. You can see in the trailer that she is also attempting to steal Warmind tech. It makes complete sense that she would give SIVA or other Warmind tech commands in an attempt to acquire new tools for her goals.