Hmm. I don't mean to go off on a tangent/hijack, but I have to say that this sort of thing is the reason I heavily restrict Resurrection magics in most of my campaigns (except the truly high-magic ones).
An ethical dilemma like this--leaving aside, for the moment, whether or not it's fair to the players--should not be easily resolved by saying "Ah, let her die, you can resurrect her later." That just strips the whole thing of an enormous amount of its inherent drama.
Nor do I necessarily believe this is the mark of a bad DM as some others have suggested, though it very easily could be. Some players enjoy ethical dilemmas, and the roleplaying challenge of the no-win scenario. So long as the DM knows that's the kind of group he's got, there's no problem.
I think it's also safe for a DM to use even if his group isn't of that variety--in select circumstances. To end a major story or a campaign on this note would, indeed, be unfair to the PCs. I think it would be okay to use a tactic like this at the beginning or middle of a story, however, as a means of upping the dramatic potential.
Still, if the players don't enjoy it, don't do it. That's certainly simple enough.