Tavion is one of those bosses that can be fun and challenging if you know how to deal with her. I found out a pretty good way to fight her. Charging her is a reckless and foolish way to deal with her. Let her come to you. When she takes a swing, sidestep out of the way and take a swing of your own. Chances are you'll get away unscathed while she'll take some damage.
She's actually a little stronger in offensive Force powers than you, so don't try to make it a Force match. Focus on your saber fighting skills and techniques. You have a big edge over her (and all other Dark Jedi you'll face in the game) due to the fact that you can heal yourself. Use Force Healing if there's ever a break in the action and don't hesitate to use your bacta tanks. (if you have any, that is) Just keep a cool head and you'll prevail.
As for cheats, you have to type in a certain command in the console to activate cheat mode. If you're using an earlier version of JO, the command is "helpusobi 1." (without quotations of course) If you've updated the game to version 1.04, the command to use is "devmapall." (again without quotations)