Do you have to enter her service to be able to carry on the light side storyline? Or is it possible to leave her without entering her service and roam the planets on your own and still achieve something?

I'm pretty sure that it doesn't matter... since the final ending depends on what you do at the end anyway, but I suppose it's possible?

There is no way to not be "in her service". At first she won't let you help her. then she causes you to be the center of attn. in the galaxy.

Oh, yes, there is if you keep giving DS answers.

 

The response when asking for your ship and "slaves" is abit different, but overall for the game it makes no difference...

 

(In her service; you are allowed to come back, atleast they say, but you can't)

(If not they won't allow you to return, no difference here though...)

You can get to a point where she just tells you to clear out by giving her mostly DS answers. That way you won't be "in her service". But it really makes no difference - the missions the plot will put you through will be just the same in any event, so don't worry about it.

 

IIRC, the light/dark side outcome of the conversation depends on a total evaluation of the entire conversation rather than individual points along the way. So if you're playing light side, you can take a few defiant or DS options along the way without consequence as long as you don't do it more frequently than the LS choices. That said, I don't consider disagreeing with Atris on adherence to the jedi code to be DS. Indeed, saying that saving thousands of lives is more important than following a rigid jedi code is more LS.

 

But it's the net evaluation of the conversation as a whole that determines whether you get LS or DS points.

Before the game starts you are "in her service" since she is the one that sets everything into motion at the beginning of K2.