I'm saddened but not shocked that everyone is piling on to this poor women's partners for not providing a fireman's belay. I would think before you sling blame around, especially if friends of the victim start reading this. Unfortunately a fireman's belay is not the great panacea that a lot of canyoneers seem to think it is. To wit:
1) Nowhere in any published accounts of this accident so far (at least that I have seen) is there mention that no fireman's belay was performed. Or, there may have been legitimate reasons for not having one in this location (such as loose rock).
2) There are legitimate questions on the effectiveness of fireman's belays. For more reading, see
this testing done by cavers.
3) Very, very few canyoneers have received training on fireman's belays, or caught a simulated fall using a fireman's belay, because simulated falls are notoriously difficult to stage safely. I think many that would try this might be surprised to find that it isn't as easy to catch someone falling using a fireman's belay as they might think it is. There is a lot more involved than "just pull the rope tight". Things aren't so black and white.
4) In my experience, most canyoneers don't know how to perform an adequate fireman's belay anyway. I can't count how many people I've seen giving these sorts of belays incorrectly. It's rare that I've seen it done right.
Check out this photo, from a website of a Zion-based company offering canyoneering courses, which illustrates how most people give these belays. Note that she is making at least three technique mistakes that I can see, each of which inhibits her ability to perform an adequate fireman's belay. Any guesses?