You previously had Robert Packwood forced to resign from the US Senate due to the extent of sexual misconduct allegations against him, including specifically his staff.
en.wikipedia.org
That was in allot of ways a very glaring example of how #metoo could apply to to politicians prior to when it hit Hollywood and the more recent phenomenon.
In other words it was quite clear that something like a sexual assault or especially rape allegation by a staff member against a politician could potentially matter politically by the time Biden was being considered for VP. The idea she assumed a bunch of people coming out with allegations like hers would not potentially be a problem for Obama's campaign seems hard to believe. (The Obama campaign could hypothetically have further investigated once they were clued in that this specific issue would be a concern, and could have chosen to drop Biden as a possible VP pick if they found enough supporting indications that this was going to be an issue without having to publicly say why.) In other words, she has inside information demonstrating the Biden was a weak candidate, and she would have actually been doing the Obama campaign a favor if anything by letting them know about this risk prior to them picking Biden and potentially getting ambushed by a bunch of allegations during the general election.