Hi, not likely a virus, & there is minimal protection in 10.5.8 & up...
About Safari 5.1.7 and Leopard Security Update 2012-003
Summary
Learn about Safari 5.1.7 and Leopard Security Update 2012-003.
Products Affected
Mac OS X 10.5, Product Security, Safari 5.1 (Mac OS X 10.6), Safari 5.1 (OS X Lion)
Safari 5.1.7 for OS X Lion, Safari 5.1.7 for OS X Snow Leopard, and Leopard Security Update 2012-003 disable out-of-date versions of Adobe Flash Player.
Out-of-date versions of Adobe Flash Player do not include the latest security updates and will be disabled to help keep your Mac secure. If Safari 5.1.7 or Leopard Security Update 2012-003 detects an out-of-date version of Flash Player on your system, you will see a dialog informing you that Flash Player has been disabled. The dialog provides the option to go directly to Adobe's website, where you can download and install an updated version of Flash Player.
Additional Information
If you need to re-enable an out-of-date version of Flash Player, you can do the following:
1. Navigate to the /Library/Internet Plug-Ins (Disabled) folder.
2. Drag "Flash Player.plugin" into /Library/Internet Plug-Ins.
3. If the browser is running, quit and restart it.
http://support.apple.com/kb/HT5271
If you or her really think she needs it...
ClamXAV, free Virus scanner...
http://www.clamxav.com/
Free Sophos...
http://www.sophos.com/en-us/products/free-tools/sophos-antivirus-for-mac-home-ed ition/features.aspx
But have her do this first...
Safe Boot from the HD, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot.
If still problems, then...
See if the Disk is issuing any S.M.A.R.T errors in Disk Utility...
http://support.apple.com/kb/PH7029
Open Activity Monitor in Applications>Utilities, select All Processes & sort on CPU%, any indications there?
How much RAM & free space do you have also, click on the Memory & Disk Usage Tabs.
Open Console in Utilities & see if there are any clues or repeating messages when this happens.
In the Memory tab of Activity Monitor, are there a lot of Pageouts?