Her original tweet, however, raises a slew of questions about who knew what and when regarding the alleged sexual assault, which Kavanaugh, President Donald Trump's nominee to the Supreme Court, has vigorously denied.
His accuser, Christine Blasey Ford, has also been invited to testify.
It was not clear where and when Ford had identified Smyth as being present at the party.
The battle for confirmation comes just weeks before congressional elections on 6 November.
Ford's lawyers have asked the FBI to investigate her charge - that a drunken Kavanaugh groped her and tried to remove her clothes at a party when they were both teenagers - before she agrees to appear at the hearing, but Republicans have refused to go along.
"I think it's a very unfair thing what's going on", Mr. Trump said. McConnell expressed confidence that Kavanaugh would be confirmed: "I'm not concerned about tanking the nomination". "And we want to get it over with", Mr Trump said.
But the letter provoked protests from committee Republicans, who disputed the claim that Ford had been asked to testify on the same panel as Kavanaugh and insisted that an Federal Bureau of Investigation inquiry was not necessary for Ford to share her "personal knowledge and memory of events". Kirsten Gillibrand, D-N.Y. "To refuse to treat this properly and try to confirm Judge Kavanaugh at any cost tells women that once again they are not important and they are not to be believed".
"It was already a "no" but now it's a stronger 'no, '" said Bonnie Mann, 29, when asked about whether her view of Kavanaugh's nomination had changed since the allegation.
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The Guardian said it had obtained a copy of the book ahead of its publication on October 2, a month ahead of the key U.S. midterm elections.
"A full investigation by law enforcement officials will ensure that the crucial facts and witnesses in this matter are assessed in a nonpartisan manner and that the committee is fully informed before conducting any hearing or making any decisions", the letter states.
Democrats have said the White House can order a more detailed FBI investigation, as occurred during the 1991 confirmation process for Supreme Court Justice Clarence Thomas after he was accused of sexual harassment.
"Requiring an FBI investigation of a 36-year-old allegation (without specific references to time or location) before Professor Ford will appear before the Judiciary Committee is not about finding the truth, but delaying the process till after the midterm elections", Sen. "If she doesn't show up, that would be unfortunate", Trump added. "Why did they wait until everything was finished and then bring it up?"
President Donald Trump gave Kavanaugh a ringing new endorsement Tuesday, saying he felt "so badly" that Kavanaugh is facing scrutiny over allegations that he assaulted a teenage girl when both were in high school.
On Wednesday, Senator Jeff Flake - who had previously said he would not decide his vote until hearing both testimonies - also called on Prof Ford to accept the Senate's invitation. "I hope Republican Voters, and others, are watching and studying, the Democrats Playbook".
"She has been deflecting death threats and harassment and trying to care for her family and determine where they are going to sleep at night".
Committee Republicans have planned for only Kavanaugh and Ford to testify, but Democrats want other witnesses, too.
Any defections from Republicans' narrow Senate majority could sink the nomination and deal a major setback to Trump.