I don't think the problem is HTTrack, although a little 
more info would help:
1.) was there a 'restart' prompt something along the lines 
of "do you want to restart? yes/no"
2.) has she run a recently updated antivirus program with 
current virus definition files?3.) is her hardware stable?  power supply
problems and 
flaky RAM and motherboards are all causes for restarts and 
crashes.
4.) what OS and other software is she using?