If you want a non-evil romance option, you can romance Shadowheart, I don't think she's evil. Same thing goes for the male companions we can romance. The devs did say that your companions alignments can change depending on your choices and if they like you enough to follow you.
I suppose we could have some metaphysical debate of "what is evil anyway?" but let's be honest, she's evil. She worships a deity that wants to annihilate everything in existence. It doesn't come much more evil than that.
