I keep wondering if it's Cochlea or Eustachia riding with them and what happened to the other one. OK, I know the question is meaningless and I'm just being weird.
It's Eustachia. Cochlea was the one who was captured and strapped upside down in a chair with a duck on her ass. When she was captured she wondered 'where Eustchia was' so... our current girl is Eustachia.