https://www.gamespot.com/articles/the-last-of-us-part-2-features-an-npc-companion-fo/1100-6460357/

The Last of Us Part 2 writer and co-director Neil Druckmann announced that Ellie will be accompanied by an NPC in the upcoming game. So far the only gameplay of Ellie we've seen is of her fighting solo against a murderous group of enemies, but apparently that isn't representative of the full game. The news broke during a Buzzfeed interview.

Druckmann didn't confirm who the NPC would be, saying, "Well, so, Ellie used to be an NPC, but she's the protagonist in this story, so the player is controlling Ellie. It's safe to say with the game that we made in the past that there will be some NPC with you in this story, even though we're not showing [the NPC] in this demo."