[Aerich]

Your party will do fine.

Suggestions are as follows (spoilers abound):

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1) Buff up before entering
2) Have quite a few AoE and "crowd control" spells memorized - movement inhibitors and enchantments like Chaos and Symbol: Hopelessness.
3) Summons can save you pain

Upon entering, you will be advanced forward, and so cannot set up a spelltrap or wall of summons first. Have one or two tanks (preferably protected against cold and mind spells) engage the dragon, while the rest of your party backs up (to hopefully avoid her breath). Get some summons up ASAP and maybe even move your tank(s) around so Ich-t switches her attack to your summons. Get movement inhibitors up quickly too, as Ich-t has numerous minions that spawn behind her. Then hammer away with AoE. Once she and her minions are down, heal up, and move west to finish up what you need to do in the area.