You will eventually need to face Bastila on the Star Forge if you play a Light Side Jedi (or a Dark Side Jedi that did not side with Bastila after the fight at the temple) in "Star Wars: Knights of the Old Republic" (KOTOR). This fight can go one of two ways: you can defeat her in battle or you can convince her to return to the Light Side. Either option will require you to fight her several times. You'll get a chance to speak with her between skirmishes to try to win her over. You will still get past her and can continue on to face Darth Malak whether you convince her to return to the Light or not.
Use the Jedi powers "Force Immunity" or "Force Resistance" if you have them. It's best to use this power before the fight begins to protect yourself from her force powers.
Use any stimulants you may have on hand. This will give you the needed boost to your dexterity to dodge her attacks as well as increasing the damage you do with a strength stimulant.
Use your med-pacs to heal and save your Force points for other offensive and defensive Force powers.
Use "Force Speed" or "Master Speed" if you have it to get in more attacks.
Equip and activate an energy shield to guard against any physical attacks she might use if you are stunned or otherwise immobilized.
Bringing Bastila Back to the Light
Tell Bastila you won't give up on her in the conversation that happens before the first fight.
Tell Bastila the Light Side is as strong as the Dark, that Malak will never let her become powerful and she's dooming herself to an endless cycle of death and destruction in the conversation that happens after your first skirmish.
Tell Bastila you won't defend yourself if she attacks you and that she isn't evil.
Tell Bastila the dark side isn't stronger than the Light, that you don't need to kill her, that you were also redeemed, that she can reject the Dark Side and that Bastila did protect you. At this point, persuade dialogue options may start to appear. Do not use them if you don't have a very high persuade score because failing at these is worse than not trying to persuade at all.
Ask Bastila to help you defeat the Sith and tell her you trust her. The final dialogue option you should select is "You won't, Bastila." Bastila will stop attacking and offer to help the republic fleet with her Battle Meditation power if you've made all the right dialogue choices.
You can convince Bastila to return to the Light Side whether or not you've romanced her. The dialogue options will be slightly different if you have.