The Two Spies

You know how there are a bunch of douchebag nobles among Ylgrin's group?
Well. They're not the only ones to look out for in Ylgrin's camp
Plenty of commoner IceWings who were brought in by their ambitious or loyal parents and don't believe in Ylgrin's dream.
And would sell her out to come back home to the Ice Kingdom.
Smallfolk can be equally shitty and conniving as nobility.

Think the most "kill all the nobles", "you're the best hope for the Ice Kingdom", "I understand you feel bad for these non-IceWings you raided, but that makes you better", "I hate how small-minded and dull these nobles are" likeable IceWing you can think of.
Everything the average reader will swallow up without question.
And have them as a spy reporting in on Ylgrin's behavior to one of the IceWing nobles.
And Ylgrin never thinks of this IceWing as a suspect at all. Because she spent too much time thinking of the nobility as suspicious, keeping them away from her intel and plans.

This one IceWing, Issegrim, is actually the one she suspected.
The picture-perfect image of an IceWing. Stoic, keeps to themself, secretive.
Not particularly arrogant or hateful, but that secretive and stoic nature makes Ylgrin thinks Issegrim is a plant put into her camp to spy on their secrets.
Whereas this spy fed Ylgrin whatever she wanted to hear perfectly.
And one day, the spy received a note back. Hunt and skin the wolf.
That night, when they were alone... the spy wrapped their claws around Ylgrin...
And cut.

Ylgrin only survived because she sensed hostile intent and moved in a way to avoid a fatal wound.
Ylgrin would've screamed, but the spy then started strangling her.
And pointing out that Ylgrin was a fool for trusting them. That that trust will end up making sure no one will suspect "someone who made every note of playing your ideal follower."
And Ylgrin almost suffocated, eyes rolling at the back of her head...
Until Issegrim and Kettrin came rushing up, Issegrim stabbing the spy's shoulder to loosen their hold on Ylgrin and twisted the spear blade, Kettrin grabbing the other arm and making sure to break it.
Kettrin explained later that Issegrim saw the note that the spy received to kill Ylgrin, and immediately rushed towards Kettrin's tent so they could save Ylgrin together, making certain their loyalties to Ylgrin through thwarting an assassination attempt.

Except... that's not true, as Issegrim tells Ylgrin.
In truth... they were a spy, sent by another IceWing noble way back during Vargrim's leadership, to observe and report Vargrim's movements, then Ylgrin's in exchange for better social status, coin and position, and perhaps even a title for their service.
A mission and role Issegrim, then, took without question.
Except... they observed Ylgrin. Saw how she operated. Thought about what they believed in. And, unlike that other spy, who did hated the nobility and the system involved, but figured it would always exist so why bother fighting it... Issegrim started to believe. Wanted to believe in Ylgrin's dream, just a little.
Enough to send inaccurate intel to the nobility.
And even take advantage of a note they got to search the other spy's belongings for a note that night.
And thwart the assassination attempt before Ylgrin died and the assassin would slip away into the night.
And Ylgrin asks Issegrim how she can believe them. Why would she believe them? How can she, after she almost died to one spy already?
And is very scared, paranoid, and more alone than she ever was.
And Issegrim says: you can't believe me. And there's nothing I can say that will get you to trust me without a doubt. But. If you want me to leave, say the word and I will. And, if you don't, I will work to make sure your dream comes true. Even if it means speaking against you. Especially so.

Ylgrin ends up telling Issegrim to leave her alone for awhile.
She needs time and space to process everything.
Issegrim still, a tiny bit, thinks Ylgrin's dream is stupid and she'll die and what's the point of fighting against the system.
But... as she notes to herself, she was never happy being a realist.

But yeah, double-whammy of spies in Ylgrin's story.
It's meant to take advantage of the anti-nobility feelings that everyone's going to read coming out of the story.