The way I see it, a naive American thought it would be great to be a real princess. But after a very short space of time, she twigged that it meant she wouldn't be able to carry on doing whatever she wanted. Being a feisty independent woman and all that, she decided that wasn't on, and walked away. Harry had a choice - go with her and his kid, or stay home and lose them both. She had him by the royal balls. Sorry, but this looks like a classic case of gold-digger to me...
As for the racism, this isn't America. No-one cares what colour she is.