In some ways, I think starting out with a system like my first A500, a system which had plenty of appeal at the time but didn't automate much of anything, and relied on floppies and user know-how to get anything done taught me that if I was going to get anywhere, I had to grab the bull by the horns and just dive in.
In that respect, we certainly had it easier, I think. We've had years to get down the basics, before the layers of abstraction started piling up to the point where it's darn near impossible to figure out what actually IS going on beyond the mysterious monitor.
I look to my little brother-in-law as an example of the problem. Back when I was his age (13) the C64 was the "in" machine. So all the cool stuff was right there. If you wanted to do any of it, you HAD to have at least a basic understanding of how the machine functioned. (You have a disk, and on that disk is an application and some data. You turn on the computer, you LOAD the application, you OPEN the data file, etc...) There were more steps required to do what you wanted, but the steps were very closely related to what you wanted to do. So it kind of built a intuition into us about what is going on behind the scenes of a computer.
But today, the Windows PC is the "in" computer. Today's cool games, applications, and files are all there. But to run it all, you just point at the data file you want and tap the button twice. The file opens. Sure, it's easier. But you don't comprehend what really happened. You're too far abstracted from what's going on. In two clicks you just caused a comparison of the data file's filetype extension to a database of known filetypes. That comparison identified which application is registered to handle that type of file. It then launched that application and passed it the filename of the data file as an argument.
That's abstraction WAY beyond the scope of what a 13 year-old can deal with, though. How do you teach the basics to someone when they've never been exposed to the intuitive difference between loading an application and opening a data file?
I mean, sure, I can give him a C64 or an A500, but it's not the "in" computer of the time. He might play with it, but he's not going to USE it for everything, like we did. There's no better way to learn a system than to be forced to use it. I learned my C64 because it was all I had, back then. The Amiga was the same thing (I sold all my C64 gear to afford my A500!). Windows, again, forced to use it -- this time for my first job. Linux: I didn't learn it, until I made a bet that I could go an entire month without booting Windows at home. Sure enough, by the end of that month, I knew quite a lot about Linux (and more about modern x86 architecture, as a side benefit).
But how DO you pass the basic knowledge and intuitive "feel" for what a computer does to someone who wants to learn it? I think that is part of what you were getting at with the idea of giving her a base A500. Certainly using one of those is much less abstracted.
But it's not very practical to try to USE a C64 or even an Amiga for modern computing. I mean, they are pretty dated systems that are not quite up to many modern tasks we take for granted. Your typical MP3 isn't exactly going to fit on an 880k floppy, ya know? Wanna check the Yahoo! mail? Hmm...... Problems... So, the machine isn't really going to get USED.
But how do you teach the basics to someone who hasn't been forced to live within their confines? That's a question that I don't know the answer to... If I did, I'd probably sell that information as a help series, or something. ;-)