[Last Pawn]

Excuse me while I climb up on my soap box here...

You're kind of going about the process of building this thing backwards. In GURPS every trait can be broken down into three parts: Fluff, Framework, and Effect. The first thing to decide on is the desired Effect of the trait; that is, what does it do? In this case, if I'm reading things correctly, the ability causes a negative reaction in others (let's say a -2). So we know that we want to start out with an effect that causes negative reactions; however, there are a multitude of such traits available: Negative Appearance, Odious Personal Habits, Supernatural Features, Delusions, the list goes on. So, how do we choose? Well, since we have the Effect determined we can move on to refining the trait by looking at the Framework, which is how the trait presents itself in the game world.

You've spelled out that the negative reaction is based on the subject's unearthly appearance. As it just so happens GURPS already has a trait that causes people to have a negative reaction based on the subject's appearance (5 levels of it in fact). Consulting Basic, page 21 and using the assumed -2 to reactions this would mean that the subject has "Ugly" for -8 points.

At this point one might be tempted to object in pointing out that the subject is in fact "Unearthly Beautiful," but that's where the Fluff comes in. Providing the description of the trait matches the Effect (-2 to reactions) and the Framework (caused by the character's appearance) it doesn't matter how the trait is described. So in this case we can rename Ugly to Unearthly Beautiful and describe it as: "A person with this trait possesses a beauty that is so un-flawed it puts the people who see it at unease." And bang, Bob's your uncle.