Re: Linux for geeks, yes
So, your sister tried "Linux" for "a week." Without knowing what distribution/desktop combination she tried that doesn't really tell us very much. I know of people who did the same thing with Windows 8/8.1. What does it mean in that case?
I've put Linux on computers for people who have no interest in computers beyond them being a means to get certain things done or access certain information. I've later asked them if they were using it because they never came to me with a problem and was assured that they were using it, and it was working fine.
The most instruction I've had to give to a new Linux user was about using Google Play rather than iTunes.