Of course the normal extreme taboos (i.e. cheating, harm to a client, animals, children, or elderly, bullying, assault, etc.).

But it all depends really. I've done something in my past that I feel is unforgivable. Would I accept her if she did it? Maybe.

Even murder I might be willing to forgive in certain situations (i.e. self-defense).

She would have had to do something heinous to make me think less of her.