As I said, she's not light. She's grey. Very grey. Many of the things she -does- approve of are quite horrific really. Hell, recently it's even become the case that on a few light/dark choices, -both- will give me positive affection.
Fact of the matter is, over time she does get more and more grey, trying to hold onto her Jedi beliefs while she slowly but surely has to concede how stupidly and blindly most of them are followed. I think it's really well done, no sudden fall but a gradual corruption over time, if you can call it that. I'm currently around 7k affection and she's now pretty much convinced that the Jedi are just as stupid as the Sith, she's in a complete middle ground, and frankly I haven't actively tried to make her darker, the option could be there.
To be honest, she fits both alignments really well, and all this crying about not being able to fully convert her is just plain silly in my honest opinion. You can still be very evil without random acts of cruelty, it's the difference between lawful and chaotic evil, if you're familiar with D&D. She doesn't like fighting Jedi, fine, you can exclude her from that. Rational thought and secrets of the force, the things she likes, can fit into an evil character just as well as a good one, it just means you need to be less of a mindless tyrant and more of a methodical, intellectual killer, who uses logic and reason to justify his motives. It's not hard, and considering we're inquisitors, we're meant to be the cunning, intelligent, forward thinking ones.
Fact is, there's plenty of ways to work her into your story whichever alignment you choose, and if you're not willing to do that, well, sucks to be you. But don't blame Bioware for a lack of compatibility, because it's frankly not true. Best advice I can give is to start thinking of yourself as an agent of the Empire rather than a purely self-serving git and she'll love you. If your RP doesn't fit that, well, you're screwed, but it's not written -anywhere- that she -has- to love you regardless.