The US is actually worse. I've been here 8 years and I'm not even a little bit closer than I was 8 years ago, to permanent residence let alone citizenship.
I have a six figure salary. I should probably just get married.
That's a long and expensive process. There seems to be a common belief that it's more or less automatic once you're married, but that's far from true in most countries, the US and UK included.
It will probably make it more difficult to go to the country where she was born. This is a problem if she wants to go back quickly, for example when someone there is sick.