Canonically, there is one statement to dispute that the idea was to have a 'young attractive woman'; Meeghat said she had been waiting all her life. Not all her adult life. This suggests that, like the Dalai Lama, the greeter of the Lord is to be picked at a very early age.
There's a few alternative readings of the same evidence which I'd like to bring up, which might argue against the idea that Meegat was the sole priestess, holding her post from cradle to grave.
1) It seems clear from the episode that it isn't just Meegat who has been waiting all her life, her people have been waiting too. Therefore, she could arguably have been speaking as one of her people.
2) She could also, as somebody suggested earlier, have been one of a number of priestesses, working a shift system (it would have been very boring for Meegat otherwise!). If Avon and Co. had turned up a day later, they may very well have met another scantily clad woman with good taste :). They could also have been like the Vestal Virgins of ancient Rome, who IIRC trained for the job for ten years, but then only held their posts for five years at a time.
3) There is also evidence that she is aware of what is going on in the outside world. She knows that there is less than a hundred of her people left. She knows that the Scavengers also die. She knows the way to the Scavenger's camp. So I'm not entirely convinced the Dalai Lama analogy is the right one.
The trouble with setting up a trap like this, on a planet contaminated with highly dangerous radiation, is that if the messiah takes too long to turn up, you eventually run out of people to act as bait. That probably explains why Meegat, as others have observed, was no spring chicken.
Shane
"Well now, no one's going to faint with amazment at that." - Avon