Have you finished everything else in the act that you can? If not, reload a save before entering the crypt and do so.
You should switch your DK to power arrows (convert normal arrows and/or visit the BF a few times to buy some).
The skeleton doll from act 1 can equip a crossbow, so can provide good support for tough fights, as long as it is kept away from melee combat. The other dolls can at least provide a temporary distraction.
If your hero runs around to distract Kiya, you may be able to rely on your DK to do much of the damage (don't recall what type of attacks she uses).
Do you have any spare skill points you could try learning the Hammer skill (or maybe Insect Swarm). Most of Kiya's resistances are pretty high, so normal weapons or bone/shadow damage would work best.
