Can you remove songs from iTunes library but still keep them on your computer?

I share my computer with my sister and she uses the iTunes mostly, I haven't put anything new on my iPod in awhile and just often times buy stuff via my iPod so haven't been plugging in to the computer for that or charging. The problem is awhile ago I did put 3 mp3 albums from rhapsody, walmart, and amazon on the shared computer and I want to keep them on there but they're showing up in her iTunes library and we don't know how to stop this. I want to take them out of there without removing them from the computer entirely, just the iTunes library. I'm afraid she'll eventually delete them on me, and I have to do a backup but haven't done that yet. We know very little about computers and I don't want to just remove them from iTunes and risk losing them totally. Can you please help? I realize this is a dumb question but I honestly have no clue. Thanks.