You are correct. Her power is with public opinion.
70% of the public, including 64% of Republicans, would like to hear from the missing witnesses. All of these arguments being tried out here and elsewhere- that the House didn’t make its case, that it’s not the Senate’s responsibility to call witnesses that the House didn’t- none of that is going to fly with the American people outside of diehard Trump supporters. Because most people want to know if what Trump is being charged with is true. And they get that Mulvaney and Bolton know the truth, and that Trump is moving heaven and Earth, with McConnell’s help, to keep them from testifying. And that looks bad. It looks, frankly, like a cover up, and no amount of argument can eliminate that impression.
So yeah, Pelosi is eventually going to have to turn over the Articles, sooner rather than later. And McConnell and the Republicans have the power to prevent witnesses from testifying- nobody can prevent them. But if they take this step they may seriously regret it.