(1) I don't understand the question because (a) no one but her ever uses it and (b) it's never going to leave the house. Is she paranoid?
(2) Does this even exist? I know ICQ (from when I had it 5 years ago) used to keep a log of any and all conversations and had to be deleted manually. It seems strange she would have this feature on her iMac notebook. I think she's using OS X.