Tess had to realize that Nasedo's treatment of her wasn't acceptable when she came to Roswell. Michael, Isabel, and Max were this close knit family along with the humans. She surely saw how the Evans and the Parkers treated their children. I know she did with Kyle and Jim.
And she had her escape when Nasedo was killed. She no longer had to live with her tormentor. Jim and Kyle loved Tess. Jim thought of her as his daughter even. Yet, she betrayed them to go to some planet she has only known in memoires. That seems a bit harsh to me. Not only did she want to go there but take the king's heir and have Max, Michael, and Isabel executed.
Max may not have been the most considerate person to Tess in the beginning. But he also became a lot nicer to her after EOTW. Still, she wants to send him to his death even though she loved him so much

I'm not unsympathetic towards Tess nor do I hate her. I actually like when she is portrayed as someone without evil motives and plots to kill. And it is true that Tess was an interesting character that had potential. I would have been emotionally scared too if I went though what Nasedo surely put her though. I do feel sorry for her having to life with a monster.
In my opinion, she was half and half.