Something occurred to me recently.
Visser One, the former, is captured and being tortured by Visser Three. Well, obviously she had to get to that point. I kind of wonder why she didn't use her time of being pursued to capture and infest Marco.
Okay, the Yeerks think Marco is dead. Visser One was out of the loop and couldn't have known about that. And even if she couldn't get to Marco, she damn well knew where Jake was and to top it off, if she infests one she got a hold of one, she had them all period.
She could have redeemed herself and saved her own ass from being crushed to death by her host's son.