I would have your daughter look very carefully for student health insurance options for her Type 1. Insulin in the US is unbelievably expensive right now. Don't know if she uses a pump or sensors too, but more costs to weigh in as well. It's doable, just need to double check she's got some sort of insurance that will actually cover the costs.
As for the other stuff, definitely wait until you get Citizenship. Then you can come back and forth and wherever.
As for cheap places to live in the UK, you'd be looking at places like Lancashire, Midlands, Northern Ireland, parts of Scotland, Norfolk, Wales, etc -not Surrey, where you're currently at, for sure!