I also used 3 x chain lightning (a spell trigger) on Melissan that put some major hurt on her. Also, ADHW works well. But make sure you cast lower resistance on her first before you follow-up with any magic attacks.
BTW, the Ravager +6 rocks! I had Sarevok with 5 stars in halberds wield it and those vorpal hits were life-savers! He killed one of the monsters (a tough one by all accounts - shan't spoil it for you) outright with the Ravager's special ability and saved my party from a nasty fight. He scored sveral on Melissan too, but despite the graphic of a successful hit she was not killed outright.
[This message has been edited by Hayashi (edited 10-09-2001).]