Child of a British parent

[Rockefeller]

Hello everyone

I recently became friends with a neighbor who is deaf so we communicate mostly by writing. His inquiry is as follows: He has a 17 year old daughter who is American citizen and was born there. My friend recently became British within the last year but stupidly he did not include daughter in all applications. The daughter came to the UK as a visitor six years ago and have remained overstayer ever since. The daughter's mum lives in US and only communicate with her over phone or email. He would like daughter to stay here permanently and regularize her stay before she turns 18 later in the year.

Does anyone know which route is best for this girl. Many thanks.

[Wanderer]

Might be difficult with the overstay...