Thank you, but I already knew these options.
I have installed the system for someone whose mind is weaker than most of us have, and for whom a one-button-solution would be easiest to remember, as she quite rarely gets to use a computer and forgets how things need to be done. Just one button on the desktop would be best. And I remembered that when using Ubuntu 5.10, I made this button for myself, because I liked the comfort of it. The command was simply halt (without sudo) and it worked. Now, when I make a button like that, it just doesn't do it.
Another thing that makes it difficult for this person to use LinuxMint is the bad DVD-support (though that might be the same with all Linuxes?). I have so far discovered only one application that does not give the strange error message about "using DVD without libdvdcss" - it's Kaffeine - but this application does not always show subtitles. Which means that different apps need to be used for different DVDs. When inserting a DVD, the system will automatically open the one that I have set to be default, but it will not work every time. Even the praised VLC gave the libdvdcss message. And another thing about DVDs - LinuxMint does not allow you to eject the disc when the application that played it is still open - even after the end of playback.
I'm sure most of use Linux-users would not see these as big problems, but for this person, they are.
Thanks for trying, anyway.
Maybe going back to an older Ubuntu or Mint would do away with some of these issues?