There is no right answer to this question. For some people, once is enough. For others, repeated exposures are required. The health of one's immune system may be the reason why some do not get it after one exposure but no one knows for sure. Statiscally, if you are sexually active you are already exposed, right? 85% is a large number not to be part of.
does it need to be repeated sexual intercourse for one to be infected or once is enough?
Most dermatologists wear gloves on their hands when treating patients and removing warts. Doesn't she? What she is suggesting is only possible if she touched her genitals within minutes after touching a GW without gloves. So yes it is possible to do this, but not probable. She picked it up years ago via sex, IMO.