The pageant has been part of Donald Trump's empire since 1996.
An arbitrator found last year that Monnin defamed the pageant when she said it was rigged with finalists selected before the live broadcast. U.S. District Judge J. Paul Oetken ruled Thursday he does not have the power to change that finding, The Philadelphia Inquirer reported.
"The court does not take lightly that Monnin is compelled to pay what is a devastating monetary award," Oetken said, while adding that he could not let sympathy sway his conclusions.
Arbitrator Theodore Katz found last year that comments by Monnin on Facebook and in an appearance on NBC's "Today" cost Miss Universe a $5 million sponsorship from BP.
In comments on Facebook Thursday, Monnin, who comes from Cranberry in western Pennsylvania, said she is not "a sore loser." She said Miss Universe officials acknowledged in sworn testimony they manipulate the judges' decisions.
Monnin resigned as Miss Pennsylvania.