My Wife is the same way.  I solved my own headaches by subnetting our LAN so she is own her own subnet behind her own router.  Allows me to keep my box free of anti-this and anti-that programs.
Her computer is constantly being wrecked.  There are probably 4 or 5 viruses on it right now and untold amounts of spyware/malware.  Even though she runs anti-virus (McAfee,..OY!), anti-spyware (Adaware, Spybot, and something else) and some other file security something or another.
I just look at when she boots it up and shke my head.  Once every 6 months, or so, it gets so bad I have to re-install the operating system.