I believe in MK II she was bad against her will but Liu Kinda brought the good out in her I guess. :) At least that is how I look at it.

Kitana was loyal to Shao Kahn and served as one of his personal assassins until she learned the truth about her past.
Now when exactly she learned the truth they never said, but it was either during MK2 or shortly before.

In MK2, Shao Kahn took over Outworld, including Edenia. He took Sindel as his wife, making Kitana his daughter. Her and Mileena were forced by Shao Kahn to become assassins for him. Kitana was always good, but she was probably threatened to be killed. Mileena had no problem because she is a clone done by Shang Tsung, who was also under Shao Kahn's control at that time. Kitana always thought Mileena was her twin. I don't know what Sindel thought being the mother and all... Kitana was never evil. Her story is in the MK2 explanation.

Goro turned good after he formed an alliance with Kitana's armies. But now at the MKD Gamecube version, Goro is evil again.

Well that make's no sense what so ever. mabye they where just bonus characters?

Yea alot of people say that gamecube version dont count. But i dont know.....

Well i fought shao kahn was dead, Because he is a bonus character in it i think.

No Kitana wasn't always good.
Shao Kahn conquered Edenia 10,000 years ago right after Kitana was born. He raised her as his own and she grew up loyal to him, serving as one of his personal assassins.
Sometime recently Kitana did finally discover Kahn murdered her father and conquered her realm and that's when she turned good.

I always thought that was kind of bitchy of her... I mean this horrible man who eats nuns for breakfast not only spares ur life but takes you as one of his own.... and u r pretty much a cold-blooded assasin.. since when do u care about life lady!!!
Hahahaha i'm yelling at a game character

Heh, I bet Mileena feels the same way....

Well, look at it from Kitana's point of view:
She could've lived in a peaceful idyllic paradise realm with parents who genuinely cared about her....only to be stolen by this nutjob who kills her father, drives her mother to kill herself, and then proceeds to turn her into a cold-blooded murderer.
And in spite of years of loyal and dutiful service, daddy-dearest tries to replace her with a clone....just in case.

Kitana's turn against Kahn started as revenge/outrage for his ruining her life and using her as weapon. She also must've felt guilt for loyally serving the murderer of her parents and helping him dominate her own people.
And along the way she evolved into the heroic princess she is today.

If you click on the MK2 icon above you can read all about Kitana in MK2 and MKT and if you read it says she was an assasin for Kahn but turned on him when she found out Mileena wasn't her true sister. So she killed Mileena then Kahn wanted to kill Kitana so Kitana went to the Queen(Sindel, her mother) and they fought Kahn and lived happliy ever after i guess(Not really, the part about the happliy ever after)