No need to resort to Regex from what you described. This can all be done in a 2-3 batches with the regular Fill Properties from Filename tool.
Steps:
0. Import all files into MC.
1. Select all files, and apply Fill Properties from Filename using a template appropriate for this filename structure: W:\ROCK A-F\Artist\Album\filename.ext
Note that this will apply the wrong tags for files that are in the other, different, folder structure. But you can ignore these, as you'll fix them in the next step(s). That'll get you 80% of the way there.
2. Now, let's get all of those z_Outtakes folders. Make a Smartlist with the rule:
[Filename]="\z_Outtakes & Live"
This will give you a list of just those files where your previous Fill Properties from Filename template didn't work right. This will let you use the Fill Properties tool again on just these to overwrite the (wrong) data you filled in the previous step, which is why you could ignore these the first time around.
3. Control-A to select all of these files, and apply a new Fill Properties from Filename template which matches this folder structure. This time, you can ignore the [Disc #] folder "tier" (assuming they don't all have that Disc part of the structure, as you indicated), because you can do those in the next step.
4. Now to deal with the [Disc #] tier of the folder structure. You didn't specify, but the easiest will be if the folders always have something prefixing the disc number. For example, if they are something like:
\Album\Disc 1\filename.ext or \Album\d1\filename.ext.
In this case, modify your Smartlist above (or make a new one if you want) with the following rule:
[Filename]="\z_Outtakes & Live" [Filename]="\Disc"
Alter that second rule to make it match only the ones that actually contain the [Disc #] tier.
If not, it is a bit more challenging, but not the end of the world. This kind of thing would work:
[Filename]="\z_Outtakes & Live" ([Filename]="\1\" or [Filename]="\2\" or [Filename]="\3\" or [Filename]="\4\")
That would capture any folder which is named only 1, 2, 3, or 4. If you need to go much higher, there's certainly a more clever way to do it, but assuming she doesn't have 16-disc sets, you should be fine with this method.
5. Now you have a list of only the files in the \z_Outtakes & Live\ subdirectories, and of those, only the ones that contain [Disc #] data in the filenames. Control-A on these and do your last Fill Properties from Filename rule to import that data.
Done. Delete the smartlists you used to make them, and construct some nice Views so she can browse her files like she was used to, and also in new and creative ways.