How long has it been since she has rebooted her system? Also, what browser is she using? She should be able to set up pop-up blockers in her browser to prevent unwanted pop-ups.
I've not heard of getting pop-ups when simply bringing up a browser.....
Have her go thoroughly through all of her browser security settings.
Firefox is anything BUT slow on Snow Leopard. Chrome is problematic though.
It has started running very slowly and has been opening pop-up windows, even on 'safe' websites - eg: university websites. Also when opening Google she has started getting pop-ups, even before starting a search.
Sounds like her machine is infected with Yontoo malware.
The machine will need to be backed up of only verified user files to a external drive, the entire machine erased and Snow Leopard then updated to 10.6.8, apps and cleaned files returned.
If you or her can't perform this function, then seek the services of a local PC/Mac tech, Apple won't do data recovery and may install a later OS X version which will slow down the machine and require all new purchases of software or even brick the machine, which out of AppleCare is a out of pocket expense to fix.
Snow Leoaprd is recieving security updates, in fact a update to 10.6.8 installs a anti-malware that blocks Yontoo malware form installing, but it appears it was already too late in your case.