NY is a strict liability state, so all she will have to prove is that sexual contact took place when she was under age. And as age of consent in force then was 18, then - no matter how enthusiastically she may have been consenting - it's a statutory rape charge
(There isn't a directly equivalent charge in the UK jurisdictions, though there is strict liability for u13s; we also have age propinquity for 13+ up to men age 18)
In NY there are a range of sexual abuse charges available in these circumstances charges possible, and it's quite possible that it'll end up as one of the lower penalty ones, as there is no evidence whatsoever he knew she was trafficked.
Her team have had to file now, because the clock would run out otherwise. I still think that PA is a bit part player in a US scandal, which needs to be kept in the news so that the rest of the whole sorry mess does not fade away