I say again this isn't even the right thread for this...
But either warrior or white mage would be the most efficient choices. warrior being the more effective on, especially if she wants to go thief as, well are extremely weak until level 15, even then they aren't that good of a DD. (edit: this part came out wrong, thief can be an amazing DD with the proper gear, subjob, and player. I've done both monk sub with H2H *pre SA* then moved onto sword with war sub, and switched between the two based on the enemies... Just didn't want to upset any thiefs out there, my brother might have my head >.>; )
I really want to go into more detail about this...
DAMN YOU BRION, QUIT TRYING TO GET ME ON THE STUFF AGAIN!