newacct

That requirement only starts on October 1. And in any case, if the OP's daughter is entering the US by land, she would present herself as a US citizen, and they would have to let her in if she can satisfactorily prove her US citizenship even if she doesn't have a passport. She would not need to present herself as a British citizen, so the ESTA requirement would not matter.

Jerseygirl

I realize that and keep saying…as long as she can prove US citizenship. If she cannot, she cannot enter as a UK citizen or use ESTA…even if crossing via a land border.

She MUST enter the US as a US citizen. Perhaps the OP could let us know what proof, if any, she has of US citizenship, ie US birth certificate/nat. cert etc.