Come on, Warlord! No, the idea of the warlord. The champion. The fighter. It filled her mind. It took a shape.
A surprising shape.
“Trap!” shouted the bald jester. “You fell for it! Get out, get out!”
The little fat clown was back. In the flower dreams, he was impotent. Here in her headspace, he wielded a warhammer and was smashing bugs on everything.
The insects hissed as a group with each strike. “Ssstay bahhhck!” they warned Betsy. “Thiss iss what I was looking fohhr!”
Jillian's thoughts and wishes given form. The ability of the form is unchained by the heroine buds. Both show that the jester is Jillian, or at least a part of her. Appearing to be a defensive mechanism, he has appeared when Jillian is near to losing herself.
Jillian tried to yell to the jester, but she still had no voice. How? How can I get out?
The blows of the hammer seemed to be making the mindspace ring and crack. Could she fly out? Out of her mind? What would happen? Could the idea of escaping get her out of here? It was all she could think to try.
This does indicate that Jillian sees herself as separate from the jester, both in the language of 'x spoke to y' and the impersonal and passive "the blows of the hammer". This does not necessarily prove that the jester is not some part of Jillian; instead it can be seen that it is a part she doesn't recognize or think on much. Also, I will concede the significance of a hammer.
“What is it?” asked the Betsy concept.
The jester was covered in insects now, and his screams were more tormented than defiant. “Get out!”
“Tool of the enemy,” snapped the insects with a crackle of chitin. “Hhhelp me kill it!”
The word choice is definitely not on accident. The capitalization of "Tool" placed at the beginning of the sentence allows it to be ambiguous. It is not evidence either way.
“Jussst hhold it down!”
The Betsy sculpture raised its arms and swam, fishlike, at the jester. She caught its hammer arm by the wrist and pinned it to the concept of an unbreakable wall. The little man was held fast against what might have been the limit of Jillian’s own comprehension.
The insects covered the jester. He stopped screaming, then stopped moving. In seconds, he was completely devoured.
Betsy drifted away, toward something like Jillian’s ideas of happiness, contentedness. Green meadows and safety. Jillian’s viewpoint began to dissolve a bit, as the insects fanned out over her mind and resumed their network of pathways.
This also has the duality of Jillian and things in Jillian's mind (not counting Betsy and Charlie, of course) as distinct forces. The wall is either created by Betsy or used by her against the jester contrary to Jillian's will.
“What was it?” asked Betsy. “A tool of what enemy?”
“The only one worth fighting,” said the insects. “Don’t ever find out. Trussst me.”
Here, "tool" is lower-case, albeit used by someone who does not know what it was. So, who does Charlie consider worth fighting? Parson is the only one Charlie has ever been known to truly campaign against and really only after Parson demonstrated free will by refusing Ruthlessness and declaring independence of manipulation.
Viewpoint-Jillian lacked the will to try anything else,
After all this ambiguity, we have the author say two important things. Jillian had acted and Jillian now did not have will to continue acting. So, what was the tool that was destroyed? It was described as: possibly residing in Aggression and Conscience (both part of the same structure according to Charlie), the shape of a warlord (Jillian's main identity), something fairly foreign to Jillian but still recognizable, something Charlie had expected and even been searching for, something that can be restrained by others and a defense that leaves Jillian unable to continue fighting.
So, is the jester an internal force of Will (or Duty, the two have an interesting relationship integral to the themes of the overall story) or an external force directed by an unknown entity?
For me, it seems certain (obvious may be too strong a word) that the jester was Jillian's will, her independence that allowed her to resist Wanda's interrogations, defy Orders and wrest victory from defeat. These are all things Jillian is unable to do in Books 1 and 2.