Since she's in pratical training, if HR asks whether she can legally seek employment in the US, say yes. Because if the company is following the law, that's the only question they can ask, they can't ask whether she has green card or is US citizen or not. Don't mention she wants them to sponsor for green card. Once in, she can try to work through the process to obtain H1, then green card either by hiring a lawyer herself or through the company's lawyer.