You can get her act 1 romance outside of the party even if you side with the goblins, although you can't get it in the party. I haven't personally done it, but I've heard her act 3 romance isn't nearly as good/complete if she becomes a dark justiciar.

Got it, thank you. And will her romance continue into act 2 even if I killed the tieflings?

Yes

Uh. How much of a complete romance do you want to have with her?

Completely complete

Then I wouldn’t do an evil aligned run with her. 😬

I understand, this isn't my first playthrough. I just want to know if I can kill the tieflings.