I am also currently trying to avoid losing Pallegina when siding with Huana. For me, VTC is not the "Rival" and I have good relationship with them/Pallegina. She was only initially exiled from VTC, but then welcomed back/returned.
Here's what I did: I tried talking to the Hazanui then declining the Queen assassination, causing her to attack me (to not lose Maia). But whenever I talk to the queen then leave the island, Pallegina leaves. Even though her departing letters says I wronged the VTC, and when I ask she says everything's fine.
Any Ideas? Is it simply not possible?