maybe sitting down with her for a while and giving her some pointers on the ins and outs of things about what is safe and what and the consequenses of her actions may help instead of going behind her back.
what age is your sis? if its just silly programs let her get on with it, if its dodgy stuff as above and install a good antivirus and spyware software and help her keep them up to date.
but this doesn't sound like a very happy set of circumstances. You don't say how old your sister is, but do you think that its a good thing to be spying on her in this way? Isn't this something that your parents should be taking care of?
I'm very much against advising anyone - particularly someone who seems fairly young - on the ins and outs of keyloggers and activity monitors, and I'm surprised that some forum members seem to think its perfectly OK to do so.
I think this is a family matter, and not something we want to be involved in.
This thread is now locked and can not be replied to.