Trylla Scott warned Picard to watch out for those parasites in "Conspiracy", but didn't even follow her own advice.
My impression was that she was supposed to have been suspect all along, ie. that she was a mole in the initial "meeting of Captains" at the start of the episode, and that it was her who sold all of the others up the river (resulting in the destruction of Walker Keel's ship). Maybe she hadn't actually been "got at" by that stage, but I'd assumed maybe she was following orders from Admirals who had
become compromised by the parasites.
There's no way to be sure, though one would think Keel would've grilled her as hard as he did Picard shortly thereafter.