Well, that's true, but there's still the 50% miss chance from concealment, right? I've also given her two ranks in Move Silently, which could mess up the players' heads a bit if she sneaks away.
Plus hopefully her undead, and (having realized how few undead Animate Dead really provides) some cultist underlings will be giving the players things to worry about as well. My thought is that if things get tough, she'd withdraw to fight another day.
(The background of this character is that one of the heroes killed her master when he was much younger, so she's out for blood... and I'd like to make her reoccurring rather than just the enemy of the week.)