Hon, in my opinion, using the Bible to justify why homosexuality is wrong is like using
Through The Looking Glass to explain why mirrors are evil.
The trouble is, it's often used as a divine way to justify a very
human belief and/or predjudice. A way to prove someone is right in what they think about the world. And in that, all the arguing in the world is futile, because for every piece of common sense you can come up with, they can find some interpretation of an obscure passage which 'proves' you wrong. As you say, such folks pick and choose which tenets they want to follow and which they conveniently ignore. It's right when it can be interpreted to agree with their own philosophy, but outdated when it doesn't. And whilever people think they have The Almighty backing them up, well... sometimes it's best to just realise that you don't
need to argue back. It's up to her to learn to think for herself and question her own predjudices rather than you to try and prove that her 'evidence' is extremely suspect.
If there's one thing I've learned here and in the big wide world, it's that you can't control or change other people's core beliefs and philosophies. Only examine and try to understand
your own, and how they relate to the wider world. When she actually meets a gay person in the flesh, and sees that they are, in fact,
not an abomination, and turn out to be one of the nicest, friendliest people she could ever hope to meet... then, maybe she will begin to question. It's easy to condemn from the comfort of an armchair.
We live in hope. But until then, here's a big hug from me *megahug*.