all u have to do is find where she moved them... whitch depending on what she did... could be very easy or... very annoying and drawn out.. its pretty simple to find the files.. and btw.. u said when u boot up.. can u boot up all the way? stupid question... let me rephrase... can u access stuff? if u can i can help.. if not im lost =)
For starters you can go into your help
and then on pick a task section click the bottom link tool,then on the left side click system configuration utility than in the box click startup scroll down and finf the programs that you mentioned Likizm\kevin bla bla bla and uncheck the box by it and restart.When windows restarts put a check in the remember box and click ok.That should fix that.
Then do a search for the file name and delete it.
and get a good regestry cleaner.
just do a system restore as desiboi said.... click start, help and support, system restore... look for a checkpoint that was before when ur niece used the computer and it will restore ur computer to how it was that time.
if you dont have a checkpoint too recent dont restore because you'll loose the programs you installed etc, but you wont loose documents, just restore if there was a recent checkpoint.