Pazienza had been out on $500,000 for killing Gustern, but Justice Felicia Mennin ordered the 26-year-old held without bail Tuesday after prosecutors made the request at her Manhattan Supreme Court arraignment.
"I am remanding," the judge said, expressing concern that the defendant is "a serious flight risk."
Pazienza showed no emotion as court officers handcuffed her and led her to a holding cell.
Earlier in the proceeding, the Fashion Institute of Technology graduate pleaded not guilty, through her lawyers, to first-degree manslaughter and two counts of second-degree assault.
Prosecutor Justin McNabney argued that Pazienza could flee now that she's been indicted on crimes for which she faces as much as 25 years in prison.
In addition, he argued, her fiancé's statements to investigators show that the March 10 attack on Gustern was an "intentional act," and Pazienza wanted to "cause serious physical injury" when she violently shoved the stranger, who weighed less than 100 pounds.
Pazienza sat stone-faced at the defense table as McNabney outlined the tragic moment that Gustern crossed paths with her alleged killer.
The defendant and her fiancé, Naveen Pereira, who were scheduled to marry in June, were celebrating the 100th day before their wedding, according to court papers.
They hit a series of art galleries, Pazienza drank several glasses of wine, then the couple got a meal from a food truck in Chelsea Park – one block from the assault, the papers allege.
A park staffer told them they had to leave because the park was closing, sending Pazienza into a rage. "[She] threw her food onto her fiancé and stormed out of the park," the papers say.
That's when Pazienza charged down W. 28th St., ran straight for Gustern, called her a "b-tch" and shoved her so hard she bashed the left side of her head, court documents allege.
Moments later, Pazienza called Pereira and asked him to meet her. She allegedly berated him for "ruining her night" without mentioning that she had attacked an elderly woman, according to prosecutors.
Before the couple headed back to their Astoria apartment, she allegedly stood in the middle of W. 29th St. looking directly at the ambulance outside Gustern's building.
Only after they returned home that night did Pazienza tell her fiancé what she had done. When he asked why, she allegedly answered that the victim "might have said something" to her, but she wasn't sure.
"That was her only explanation," a court document alleges. A few days later, after Pazienza saw a newspaper report indicating that Gustern had died, her fiancé told investigators she became "really scared and nervous" and fled New York City, the papers say.
She deleted all her social media – including her wedding website — and hid out at her aunt's house, Pereira allegedly told authorities.
After police knocked on the door of her parent’s Long Island home, Pazienza turned herself in.
A medical examiner testified in the grand jury that the blunt force wound to the top of Gustern’s head required "substantial force."
Pazienza's defense lawyer John Esposito argued that the facts of the case had not changed since her arrest and there were no grounds to change her bail conditions.
Esposito said that she is living with her parents and is receiving counseling "on several issues" but has no psychiatric diagnosis. Her mother was in the courtroom, as were several family members and friends of Gustern.
"I'm sorry for her, I'm sorry for her parents, but what she did needs to have consequences," said Gustern's friend, Morgan Jenness, who applauded the judge's decision to jail Pazienza.
She's due back in court July 26.