armor is very useful, if you're not good that is.
I mean, +4 to saving throws kicks major ass, not to mention 20% MR. 
As for tips to kill Adalon; there are only two:
->use skeleton warriors, they can hold out really long aginst her. Majority of her spells (and breath ofcourse) are cold-based and as well know, most undead are immune to cold. As are skeleton warriors. You'll need them to keep her busy, certainly in the first 2-3 round to take the cold damage etc.
->take her out FAST: it's better to do an all-or-nothing attack with everythging you've got than to slowly wear her down: she has a tendency to quickly cast "heal" on herself, and more than once. It's kinda a bummer to see a dragon go from "near death" to "uninjured".
And ofcourse, if you're gonna use magic, use fire-based magic. Melf's meteors come to mind for the mages. Use physical force overall tho; she's not too big a spellcaster, more of a brawler.
uuugh...