In Windows Explorer's menus, "Tools > Internet Options", select the Advanced tab and scroll down the list of 'Settings' until you find a box for "Do not save encrypted pages to disk". Make sure it is ticked, because this will prevent secure "https" pages being saved in the Temporary Internet Files folder.
It is also essential to maintain and run up-to-date AntiVirus, Anti-Spyware and Firewall software. Never keep details of passwords in the PC.
Another option is to use an alternative web browser, such as Firefox, which is more secure than Internet Explorer, provided her account can be aaccessed by browsers other than I.E.