You were a shape shifter, and the team's strongest member.

You'd gotten pretty hurt on a mission, and you shifted into an animal. You were hiding somewhere in the base.

Price, Soap, and Ghost were all trying to figure out where you were.

They were all undoubtedly worried about you. They'd grown to see you as family, as a daughter of sorts. Even Ghost, who was normally cold and silent, had grown close to you. So your absence worried them beyond belief.