Former students remembered her as fierce, supportive and loving. She taught out of her apartment, with a grand piano in her living room and an electronic piano in her bedroom, where her pupils practiced vocal exercises so as not to disturb her neighbors.

Melinda Pope DeRocker said she first turned to Ms. Gustern in 1997, when she was looking to return to singing after becoming a music director. Ms. Gustern taught her how to open up her vocal range, she said. When Ms. DeRocker had her thyroid removed 11 years ago, it was Ms. Gustern who gave her the confidence to sing again without fear.

“She didn’t just change the voice,” Ms. DeRocker said. “She changed lives.”

Upon hearing of Ms. Pazienza’s arrest Tuesday, Ms. DeRocker said she broke down in tears.

“Relief was the biggest emotion, but then it was right back into sadness,” Ms. DeRocker said. “Frankly, I felt sad for this woman. With one shove, she’s ruined her life.”

Relatives of Ms. Pazienza could not be reached for comment.

A LinkedIn profile for Ms. Pazienza, which had been taken down as of Tuesday afternoon, listed her as an event coordinator for Roche Bobois, a high-end furniture company. A spokeswoman for the company confirmed that Ms. Pazienza had worked there but resigned last December.

Ms. Pazienza stood silently during her arraignment hearing Tuesday, handcuffed behind her back as the assistant district attorney, Justin McNabney, read off the charges against her. Mr. McNabney said that after the shove, surveillance footage showed Ms. Pazienza spent more than 20 minutes in the area, having a “physical altercation” with her fiancé and watching the ambulance arrive at the scene.

Though Ms. Gustern was small in stature, at about five feet tall, she was strong and healthy for her age, students said. Annie McGreevey, who had been seeing Ms. Gustern once a week for the past year, said she was a fast walker and lifted weights that she kept in her bathroom.