I work at a local university and part of my job is tutoring freshman math. The first thing they do when confronted with a problem they don't understand is reach for the calculator. They are usually baffled at my suggestion that they do the math in their head to visualize what's happening in the problem.
BTW: When you nerds talk about linux being the solution to every problem you sound like people in the early eighties talking about checkbook balancing as the ultimate reason why one should own a personal computer. If your sister could use a laptop buy her an apple or a PC with WINDOWS. There's no need for you to control her experience by dictating some restricted machine that you wouldn't use yourself. I use ubuntu on my main desktop machine and I still don't think it's quite ready for prime time.