Say you're Ethan and you're stuck in another conspiracy (as we know so far) and Chris has seemed to gone rogue.
Imagine if there as a shadowy figure helping you in the backround. Dropping you clues, saving you from death, and tracking your movements. A mysterious stranger.
then at the end it's revealed to be Sheva, on her own mission to stop chris and secure intelligence for a similar situation going on in West Africa.
It's a shame she was one of two protagonist in 5 and has never been mentioned again, why?