Is She Forbidden? in General Randomness

So I have recently found myself crushing on someone and I’m not too sure if it is right. As far as I know there are no laws against it here in America and even the Bible, which is full of “Thou Shalt Not’s” has nothing to say against it. But it seems wrong. And I can just imagine the looks we would get trying to explain it to people.
You see, she is my cousin’s 20 year old daughter. We’re both over 18 so that is legal and we are far enough apart, genetically speaking, that our children shouldn’t be deformed.
So you in internet land, what is your opinion of this relationship?