Who is Ellie? During the entire game, she has never been touched by a single necromorph.
Think about it!
When we were in the food court, and the tank came after Isaac, Ellie and Stross were fighting for their lives. Who said they were after Ellie? They could have easily just gone after Stross.
And during the scene when you have to fight through a nest of necromorphs to get to the necromorph sector, why didn't the necromorphs come after her inside the machine?
This is strange... What do you guys think?