Any advice on her? I managed to kill her once, how I don't know, but I lost my cleric in the process and then got everyone else killed mopping up the yuan-ti. Any good strategies?

take your thief (you do have a thief dont you????) equip thief with fire weapon such as fire sword or the fire dagger. Sneak up on her, stab and run like hell. repeat until she is medium well.

eric out

Actually, I did this -- snuck in with my thief invisible and disarmed the traps. Then got in to start the dialog. Ran back out into the corridor. By the time she got out to me, the stinking cloud spell had run out, so I could get in close to her. The skeletons and zombies she summons really don't pose much of a threat once removed from the support of the other yuan-ti in the main chamber. So everybody ganged up on her and I had her down in a few rounds. Then it was just a matter of mopping up in the chamber, taking out the priests first, then the rest -- they're not as tough without the support of their goddess. All in all a cool battle with some neat rewards for your hard work. Off to the Severed Hand!

Hmm, I don't know why people had trouble with her, I killed her in one try!

I just ran in there with my whole party. I found that my Archer using Arrows +1 didn't work on her, but switching to Arrows +2 did, although people claim she couldn't be hurt by even +2 weapons. Perhaps it was weapon type that did it? I just had my Fighter and Paladin take on the baddies on the side hand to hand, my cleric casting her spells (I think it was Recitation, then Prayer, then Chant, then she attacked everyone) while my Mage took out people with spells and my Bard using his crossbow. The Archer is actually a Fighter/Thief. 3 of my guys are Elves, the Fighter is Dwarven, and Bard is a Half-Elf, and of course the Paladin was Human.

When I fought her I just hasted my party, cast prayer and beat her in less than 20 seconds. I don't think she even hit any of my characters once. All my weapons were +2.