I can't say this IC because Kuzan really wouldn't know. However, Lia would probably realize this so hopefully this doesn't count as metagaming
We've already discussed how Lia is our big glass cannon. While it's true fireball, etc., probably won't be much good, magic missile is always a useful spell, so maybe just prepare it. Being able to hit every time no matter what is nothing to shake a stick at. And even if it's
just magic missile, at least we'll be doing some damage to it every turn. Plus, you can use a higher-level slot to prepare a lower-level spell, so at the very least, I think it'd be better off for Lia to put magic missile in slots ordinarily saved for scorching ray/fireball.
Besides, most of us are wearing armor of some kind, so mage armor won't be as effective as it could be. As far as buffs go, Kuzan and Andre have tons and tons, and that is pretty much their role in combat -- casting buff after buff. A little more is always nice, but Lia's in a much better position to just go extreme blaster on the beast with magic missiles.