Knowing the compulsion weave and how it works is no protection against it in itself. Graendal was able to place both Moghedian and Cyndane in compulsion when they visited her. Add to this the fact that Halima would have been channeling saidin, and Egwene could have been compelled right there in the camp while she was asleep and woken up with no idea that she now had saidin compulsion in her brain.



Egwene is already distrustfull of Rand. For a person to suddenly notice that she is just a little bit more distrustfull today than she was yesterday, would require a level of self-reflection that I don't believe Egwene (or anyone else for that matter) has. Halima would have had plenty of time to keep any compulsion small and subtle and adding to it slowly over time and keeping it undetectable that way.

Not to mention the fact that it would be simple enough to add another subtle compulsion that would make Egwene ignore the first one. That might even be supported by the fact that not once did Egwene even suspect Halima of anything despite the fact that she was the only one who could rid her of her headaches.

And was Aran'gar seriously punished anyway? Compared to what happened to Moghedien(Mindtrapped and horribly tortured) or Semirhage (Abandoned by Moridin and then sacrificed by the DO), it seems Aran'gar was not punished all that severely. Maybe her punishment was lighter than theirs, because she did partially succeed in influencing Egwene, even if she failed to prevent the tower from reforming.