Dr. Ford actually told others years ago, which has been confirmed. Since sexual assaults are typically not done in front of an audience, and since the only other person in the room was allegedly a friend of Kavanaugh’s, she might have considered her case hopeless whereas to not file charges. This is not at all unusual in such cases.
So, why now? Don’t know for sure but my guess is that if something like that happened to you, heaven forbid, and then you saw that same individual who assaulted you being elevated to the highest court in the land that often deals with crime, might you not maybe be upset enough to think “Enough!” and break your silence?