I didn’t get the impression that she expected the water to do anything. She was just drinking it to keep it from being profaned in the airport trash. After all, unlike the water hawked on the lourdes-water.org site mentioned in the article, this water was *known* by the passenger to be the genuine article, since she procured it on site in Lourdes.
There is no implication from the context that she expected a cure or anything from the water. Indeed, she may have been bringing it home for someone other than herself.
But I would disagree with you about WHY she was bringing the water back. It is obvious there is a reason for purchasing/obtaining "holy" water from one place in regards to other places. Your impression or not does not change the fact that she brought the water back for a special reason. Why that water as compared to any other "holy water"? She expected the water to do something, to be something different than other water. Your argument just does not make sense.