The only way to stop bullying is to stand up to bullies. I know it's difficult and there may be consequences, but I really believe the right way to handle this is to gather up a bunch of these stories and publish them with full disclosure of the names of people involved. You don't change a culture of harassment by quietly warning people about who is a harasser. You change the culture by ostracizing people who behave…
Devil's advocate: We should be careful about doing this as we could end up harassing someone over a false claim or overreaction. In this case, maybe some discretion is necessary. I do support public humiliation in cases that are well documented and blatant.
Look at what the founder has to lose in a false accusation: not only will their startup likely not be funded, they may have trouble getting work in any capacity. (Historically, women who have made sexual harassment charges have had trouble getting future jobs.)
She has more incentive to cover it up than to expose the harassment.