Why now accuse the Supreme Court justice nominee?

I wonder whether Brett Kavanaugh, nominated for the US Supreme Court, ever thought or feared that an alleged incident 30 years ago when he was a teenager might come up during the Senate committee hearing into his new prospective job? He has denied the accusation made by a former high school female pupil that he held her down on a bed, tried to remove her clothes and put his hand on her mouth when she began to scream. The judge has said no such incident occurred. But the female student, now a professor who has identified herself as Christine Blassey Ford insists it did take place and she is willing to give evidence about it to the Senate Judiciary Committee. Now if this claimed sexual assault took place, it must be right for Professor Ford to be given the chance to appear before the committee deciding on whether to approve the appointment of Kavanaugh to the Supreme Court. He can then give his side of the story and the senators can make up their own minds. That's called justice. But the first question should surely be: "Why Professor Ford are you making this accusation now 30 years later? Why didn't you mention it at the time or way back when your alleged attacker was rising up in the judicial world?" Well, the answer to the first question is all about youth and fear. If the incident took place then she must have been terrified and too scared to tell anyone in case they thought she was just being a sneak or making it up for some personal reason. But later, was there not a moment when she must have thought she should say something? Whatever the truth of the accusation, is it the fact that Kavanaugh has been selected by Trump that has provoked her into going public after 30 years. If she is a victim of a sexual assault I am on her side and she deserves to be heard. But if there is anything political in her coming forward - ie she hates Trump - then it may have to be treated with care. I make no judgment and I am no fan of Trump, but such an accusation at this particular time makes me wonder whether the presence of Trump in the White House is behind it. The senators at least need to know what her motivations are, apart from wanting to tell everyone about an incident 30 years ago.