I feel badly for you, but 2 of the 3 answers aren't what you want to hear, and I am afraid you are just listening to what you want to hear to try to force it to work. China is older and she doesn't need a young rude dog up in her business, that she may be getting to old to defend herself against. Not all dogs love each other, Labradors are usually pretty good with each other, but other breeds sometimes not.
I really sincerely feel that you deserve a dog that fits better into your lifestyle too, and that it's the best interests of everyone, if you take Amber back. The longer you keep her, the more attached you will become, and the higher the chances of a more serious fight, since things aren't cooling off in the days since you brought her home. I am pretty surprised the shelter allowed you to bring Amber home with a nervous/too scared (China) to get out of the car dog with you. I know you adopted her with the best intentions, I am sure the shelter will take her back and find her a good home. You absolutely will not be giving up on her, you will be giving her the gift of a better situation and home. I am sure Amber is stressed too.