Well, as mentioned, after several years and many a misadventure, I've given up on RAIDZ for Mac and decided on good ol' dependable RAID 10. Today I finally got around to building the array...and realized I'd forgotten how to do it.
Fortunately, it's well-documented on Apple's site. The trick is that you build all 3 RAID sets (two RAID 1/mirrored, one RAID 0/striped) at once; you can't build the two RAID 1 sets and then add them both to a RAID 0 set afterward.
Course, the next step is to copy all the files off her old drives onto the new array, and that is going to take a lot longer -- especially since I don't have a spare FireWire 800 (or even 400) enclosure and I have to use USB 2. It'll be at that copy all night, and that's just the first drive. Which means no rebooting to play The Walking Dead like I'd hoped.
So it goes -- my wedding's in three weeks and I need to get this done so Gran can put a video together for it.