The Divine Value of Turn Undead

so 1 and 2 HD undead, aka skeletons and zombies, are just marginally tougher than similar 1 and 2HD foes. They hit and damage the same, but they aren’t vulnerable to some common countermeasures to large groups of enemies like sleep. You’ll probably be fine on that front, maybe see a few more deaths than usual, possibly the same if the party gets creative with Protection From Evil in hallways.

The problem comes with wights, wraiths, and everything beyond that. Level drain is horrible, one of the most awful things that can happen to a character. Be prepared for players who have sacked away large reserves of XP to just retire characters that suffer too many level drains. This is where turn undead becomes relevant, and it along with the aformentioned protection from evil (by virtue of disallowing the touch attacks that cause level drain) are one of the few countermeasures. If you’re sticking to mostly 1 and 2 HD undead, you can probably get away with not having turn undead available, and if you really wanted to you could fall short of the recommended power replacements.

That being said, I’d recommend being careful about how much effort you put into the priestess. Even before your modifications, the class is at risk of being a dedicated NPC class, and unless some way to directly contribute to battle is swapped in, only someone who genuinely enjoys playing the most passive, healing/buffing oriented character will play as one.