Yes, it is built in to the OS, no need for any extra software, Mac OS X comes in a host of languages right out of the box.
Just set up a new account for her, then go to international preferences to turn her account into Korean
Changing the system language in Mac OS X « David’s logbook
if you do a clean install of Panther, then if you select Korean in the initial set-up, even the login window will be in Korean