I've read most of the recent Texts, and I'm not seeing anything obvious. I do notice some specific facts:
1) Bart popped as a Viscount, and Wanda observed this Level 1 being called such.
Back in Diecast, during the morning after. This strongly suggests FAQ is a Royal side. I know that it is a popular opinion that non-Royal sides can pop nobles, but there is no text that suggests this. Wanda has no title. She is called "Lady", but never Countess, Baroness, etc., and we now know through Marika that noble females do have titles, and are not simply "Lady". While non-Royal sides could gain noble Units by Turning or contract, a Level 1 Warlord wouldn't be powerful enough for such a deal or bother, so the chance FAQ gained him by means other than popping are low.
2) Jillian protests that she has been titled Princess and never stated FAQ was Royal.
What she fails to mention is that she never mentioned Marika was a Countess or noble. The previous text is anecdotal, rather than quoted, so we do not get the specifics of exactly what Jillian said in her description of Marika. It is speculation that she mentioned her as Countess, but I think it's not a huge reach to conclude that Jillian simply failed to mention to us that she stated it. Since "Countess" is the first word on the gravestone, I'd think she would react to that first, and all the rest later, if she had not mentioned Marika's title.
3) The timing of Marika vs. Jillian's popping.
Jillian stopped being called Princess 200 turns before capture. Jillian popped a over 700 Turns before Warchalking, but since the resolution is in the 100's, less than 800. We do not know the passage of time from fall of Haffaton to Warchalking, so we can't plant it firmly. I am resistant to the idea it was measured in 10's of Turns, and ore inclined towards a few hundred. With Marika 440 Turns old at death, we only have 500-600 left to work with, so that strongly suggests Marika popped before Jillian. Marika as Countess promotes the idea that her Ruler is Royal, based on Nobility on popping only for Royal Sides, and that suggests Jillian is Noble or Royal, since she popped second and does not mention a Rulership change. FAQ would need to lose its King and replace with a non-Royal to pop Jillian as a normal Warlord.
Jillian catching and passing Marika in levels also suggests a faster leveling rate, further suggesting Royal status.
The title "Princess" is the only title that an Heir would fear in the field, if her status is to be a concern. Other "Noble" titles would not strongly indicate Heir status, and the higher ransom such a capture would reflect. Countess no more suggests Heir status than "Nosepicker" does.
4) Hedda and Chip are missing
Bart is uncroaked, but Jillian does not note any other named FAQ soldiers. Remarkably, she does not think at all about the possibility of any other FAQ soldiers being tortured more normally in a dungeon to Turn them. Seeing her Princess title should jump to the conclusion that they were tortured and broke, if she was unaware of their Fate.
I think the only ways Wanda could get to the conclusion Jillian is Royal accurately are:
1) Haffaton tortured and broke Hedda or Chip (using more normal methods)
2) Nobles can only pop for Royals
3) Wanda has been talking in her delusions