In the existing court cases they will argue they need the Mueller grand jury materials to prepare the house managers for the defense of the impeachment. And they will win unless the impeachment was dismissed or Trump was acquitted before the court rules. That is their plan. She is not holding up the process to make herself look good or for some imaginary leverage over the Senate which she does not have.
She’ll lose the argument immediately.
They argued and prepared their case in congress, and that’s the end of their part of the case.
Nothing else for Pelosi to do.