I'm not sure if you have Ascension installed .. i dont think so, but that's not really a problem. I do have ascension installed, which has an improved mellisan.I'm not sure what the changes are, but I'll give you her immunities, which should be pretty much the same without Ascension.
AC, THAC0, HP, Resistances etc. SPOILERS below !!!!!! only spoilers after this
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General Info
Base Armor Class = -10
THAC0 = -7
500 HP
4 attacks per round
lvl 30/30 cleric/mage
Now she has a few rings in her inventory that make her immune to ..stuff ..
I dont have IEEP, so I cant tell what it is, but its probably your random immunities to Imprisonment and such.
As for her Rsistances ( the fun part ) :
Acid : 50
Cold : 50
Electricity: 50
Fire : 50
Crushing : 75
Piercing : 75
Slashing : 75
Missile : 75
Magic : 70
Magic fire : 50
Mafic cold : 50
Its basically just a bad idea to attack her with any elemental-based spells.
I guess Abi-dalzim's Horrid Wilting and Skull trap are your spells to use.
Anywayz, have fun